feat(preview): floating modal + async render + raw-first toggle (#40)

Three intertwined fixes to the preview experience.

## Floating modal (Space)

Was: full-screen takeover that didn't feel like a modal.
Now: centered floating box (~80% × 80%) with rounded accent border,
overlaid on the still-rendered underlying view.

Uses `charmbracelet/x/ansi.Cut` for cell-aware substring operations so
the overlay survives ANSI escape codes. `padBlock` normalises the
background to a full screenW × screenH grid first — without that,
short matrix-view rows produced a "left strip" of width 0 and the
modal drifted to column 0 on those rows.

## Async glamour render

Was: glamour was invoked inside `View()`, blocking every keystroke on
the cold-render path even with a cache. j/k felt laggy in side mode.
Now: rendering is dispatched in a `tea.Cmd` (goroutine), result comes
back as `PreviewRenderedMsg`, the model stores it. `View()` only ever
reads the cache. `ensurePreviewRendered()` is called from key handlers
that change the relevant inputs (preview toggle, j/k, resize, scan).

This is the canonical Bubble Tea pattern for expensive work and the
reason `bubbles/spinner`, `glow`, etc. stay responsive.

## Raw-first + r toggle

Was: preview opened directly in glamour-rendered markdown.
Now: opens showing the **raw file content** (instant — just split
`rec.Raw` on newlines). Pressing `r` toggles to rendered. The glamour
goroutine is dispatched the moment the preview opens, so the cache is
almost always warm by the time the user presses `r`.

Added `Raw string` to `SkillRecord` to store the original file bytes
(byte-exact, not reconstructed from frontmatter + body).

## Keymap

- Space   — toggle modal preview
- Shift+P — toggle side-panel preview
- r       — toggle raw ↔ rendered (preview only)
- R       — re-scan
- j/k     — scroll preview (when it owns input) else navigate skills
- Tab     — swap focus between skill list and preview pane (side mode)
- Esc     — close any preview

Toolbar's `r` label is dynamic: shows `→ rendered` when in raw and
`→ raw` when in rendered, so the user always knows the current mode
and what r will do next. Avoids fighting lipgloss layout to put a tag
in the header.

Tests cover the keymap state machine end-to-end (space, P, r, Esc,
cross-switching).

Author: heidihowilson

go.mod

@@ -7,6 +7,8 @@ require (
 	github.com/charmbracelet/bubbletea v1.3.4
 	github.com/charmbracelet/glamour v0.8.0
 	github.com/charmbracelet/lipgloss v1.1.0
+	github.com/charmbracelet/x/ansi v0.8.0
+	github.com/muesli/reflow v0.3.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
@@ -16,7 +18,6 @@ require (
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
 	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/charmbracelet/colorprofile v0.2.3-0.20250311203215-f60798e515dc // indirect
-	github.com/charmbracelet/x/ansi v0.8.0 // indirect
 	github.com/charmbracelet/x/cellbuf v0.0.13-0.20250311204145-2c3ea96c31dd // indirect
 	github.com/charmbracelet/x/term v0.2.1 // indirect
 	github.com/dlclark/regexp2 v1.11.0 // indirect
@@ -29,7 +30,6 @@ require (
 	github.com/microcosm-cc/bluemonday v1.0.27 // indirect
 	github.com/muesli/ansi v0.0.0-20230316100256-276c6243b2f6 // indirect
 	github.com/muesli/cancelreader v0.2.2 // indirect
-	github.com/muesli/reflow v0.3.0 // indirect
 	github.com/muesli/termenv v0.16.0 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect

internal/app/model.go

@@ -84,6 +84,14 @@ type ScanDoneMsg struct {
 	Err    error
 }
 
+// PreviewRenderedMsg carries a finished glamour render back to the event
+// loop. Dispatched by a tea.Cmd running in a goroutine — never block
+// View() or Update() on the actual render.
+type PreviewRenderedMsg struct {
+	Key   string
+	Lines []string
+}
+
 // Model is the single source of truth for all app state.
 type Model struct {
 	// Infrastructure
@@ -110,6 +118,14 @@ type Model struct {
 	Focus       FocusPanel
 	PreviewMode ui.PreviewMode
 
+	// Preview state. PreviewScroll is the current vertical scroll offset
+	// within the preview body. PreviewRendered toggles between raw file
+	// content (default — fast, no glamour pass) and the glamour-rendered
+	// markdown (R toggles). Preview caches the expensive rendered output.
+	PreviewScroll   int
+	PreviewRendered bool
+	Preview         ui.Preview
+
 	// Operation overlay
 	OpMode   OpMode
 	OpSkill  *scan.SkillRecord

internal/app/preview_keymap_test.go

@@ -0,0 +1,82 @@
+package app
+
+import (
+	"testing"
+
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/heidihowilson/skillscope/internal/harness"
+	"github.com/heidihowilson/skillscope/internal/ui"
+)
+
+func key(s string) tea.KeyMsg {
+	return tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune(s)}
+}
+
+func newKMTestModel() *Model {
+	m := NewModel(harness.Context{})
+	m.Width = 100
+	m.Height = 30
+	return m
+}
+
+func TestPreviewKeymap_Space_TogglesModal(t *testing.T) {
+	m := newKMTestModel()
+	if m.PreviewMode != ui.PreviewOff {
+		t.Fatalf("initial PreviewMode = %v, want Off", m.PreviewMode)
+	}
+	m.Update(key(" "))
+	if m.PreviewMode != ui.PreviewModal {
+		t.Errorf("after first Space: PreviewMode = %v, want Modal", m.PreviewMode)
+	}
+	m.Update(key(" "))
+	if m.PreviewMode != ui.PreviewOff {
+		t.Errorf("after second Space: PreviewMode = %v, want Off", m.PreviewMode)
+	}
+}
+
+func TestPreviewKeymap_LowercaseP_DoesNotTriggerPreview(t *testing.T) {
+	m := newKMTestModel()
+	m.Update(key("p"))
+	if m.PreviewMode != ui.PreviewOff {
+		t.Errorf("lowercase p should no longer open preview, got %v", m.PreviewMode)
+	}
+}
+
+func TestPreviewKeymap_UppercaseP_TogglesSide(t *testing.T) {
+	m := newKMTestModel()
+	m.Update(key("P"))
+	if m.PreviewMode != ui.PreviewSide {
+		t.Errorf("after first P: PreviewMode = %v, want Side", m.PreviewMode)
+	}
+	m.Update(key("P"))
+	if m.PreviewMode != ui.PreviewOff {
+		t.Errorf("after second P: PreviewMode = %v, want Off", m.PreviewMode)
+	}
+}
+
+func TestPreviewKeymap_CrossSwitching(t *testing.T) {
+	m := newKMTestModel()
+	m.Update(key(" "))
+	if m.PreviewMode != ui.PreviewModal {
+		t.Fatalf("setup: PreviewMode = %v, want Modal", m.PreviewMode)
+	}
+	m.Update(key("P"))
+	if m.PreviewMode != ui.PreviewSide {
+		t.Errorf("Modal + P should switch to Side, got %v", m.PreviewMode)
+	}
+	m.Update(key(" "))
+	if m.PreviewMode != ui.PreviewModal {
+		t.Errorf("Side + Space should switch to Modal, got %v", m.PreviewMode)
+	}
+}
+
+func TestPreviewKeymap_EscClosesAnyPreview(t *testing.T) {
+	for _, start := range []ui.PreviewMode{ui.PreviewSide, ui.PreviewModal} {
+		m := newKMTestModel()
+		m.PreviewMode = start
+		m.Update(tea.KeyMsg{Type: tea.KeyEsc})
+		if m.PreviewMode != ui.PreviewOff {
+			t.Errorf("from %v, Esc should close to Off, got %v", start, m.PreviewMode)
+		}
+	}
+}