refactor: move source packages into app/ directory

[umputun]

Move all Go packages (annotation, diff, highlight, keymap, theme, ui) and entry point into app/ directory, matching the layout used in secrets and cronn projects.

• cmd/revdiff/main.go → app/main.go (no more cmd/)
• all internal import paths updated with /app/ prefix
• build configs updated (goreleaser, makefile, zed tasks)
• dropped go install instructions (binary named app after move, not worth documenting)
• removed root llms.txt duplicate, kept site/llms.txt as sole copy
• removed stale stdin-scratch-buffer plan file

[Copilot]

Pull request overview

Refactors the repository layout by moving the Go entry point and all first-party packages under app/, and updates build tooling + documentation accordingly to match the layout used in related projects.

Changes:

• Move cmd/revdiff and all Go packages into app/ and update internal import paths to include /app/.
• Update build/run configs (Makefile, .goreleaser.yml, .zed/tasks.json) to build/run from ./app.
• Remove/adjust installation docs and delete redundant/stale documentation files (llms.txt, old plan).

Reviewed changes

Copilot reviewed 31 out of 60 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
site/llms.txt	Removes obsolete go install .../cmd/revdiff instruction.
site/docs.html	Removes obsolete “Go install” section from site docs.
README.md	Removes go install installation path to avoid documenting the new ./app binary naming mismatch.
Makefile	Builds ./app from repo root and adjusts site target behavior.
llms.txt	Deletes root duplicate; site/llms.txt remains as single source.
docs/plans/completed/20260407-move-code-to-app.md	Adds completed plan documenting the refactor steps/results.
docs/plans/2026-04-06-stdin-scratch-buffer-review.md	Removes stale plan file.
CLAUDE.md	Updates project structure and path references to app/....
app/ui/styles.go	UI styles implementation under new app/ui path.
app/ui/styles_test.go	Tests for style normalization and construction.
app/ui/search.go	Search input/match navigation logic under new app/ui path.
app/ui/model.go	Updates internal imports to github.com/umputun/revdiff/app/....
app/ui/model_test.go	Updates internal imports to github.com/umputun/revdiff/app/... (including mocks).
app/ui/mocks/syntax_highlighter.go	Updates mock import path to app/diff.
app/ui/mocks/renderer.go	Updates mock import path to app/diff.
app/ui/mocks/blamer.go	Updates mock import path to app/diff.
app/ui/mdtoc.go	Updates import path to app/diff.
app/ui/mdtoc_test.go	Updates import path to app/diff.
app/ui/filetree.go	File tree implementation under new app/ui path.
app/ui/filetree_test.go	Tests for file tree behavior and rendering/truncation.
app/ui/diffview.go	Updates import path to app/diff.
app/ui/diffview_test.go	Updates import path to app/diff.
app/ui/collapsed.go	Updates import path to app/diff.
app/ui/collapsed_test.go	Updates imports to app/annotation and app/diff.
app/ui/annotlist.go	Updates imports to app/annotation and app/keymap.
app/ui/annotlist_test.go	Updates imports to app/annotation, app/diff, app/keymap.
app/ui/annotate.go	Updates imports to app/annotation and app/diff.
app/theme/theme.go	Theme implementation under new app/theme path.
app/theme/theme_test.go	Theme parsing/dumping/loading tests under new app/theme path.
app/theme/bundled.go	Bundled theme definitions under new app/theme path.
app/main.go	Moves entry point to app/main.go and updates internal imports to app/....
app/main_test.go	Updates imports to app/diff and app/theme.
app/keymap/keymap.go	Keymap implementation under new app/keymap path.
app/keymap/keymap_test.go	Keymap tests under new app/keymap path.
app/highlight/highlight.go	Updates import path to app/diff.
app/highlight/highlight_test.go	Updates import path to app/diff.
app/diff/testdata/simple_remove.diff	Adds/moves diff parser fixture under app/diff/testdata.
app/diff/testdata/simple_add.diff	Adds/moves diff parser fixture under app/diff/testdata.
app/diff/testdata/multi_hunk.diff	Adds/moves diff parser fixture under app/diff/testdata.
app/diff/testdata/mixed_changes.diff	Adds/moves diff parser fixture under app/diff/testdata.
app/diff/testdata/empty.diff	Adds/moves empty diff fixture under app/diff/testdata.
app/diff/testdata/binary.diff	Adds/moves binary diff fixture under app/diff/testdata.
app/diff/stdin.go	Adds/moves stdin-backed renderer under app/diff.
app/diff/fallback.go	Adds/moves fallback renderer and context readers under app/diff.
app/diff/exclude.go	Adds/moves exclude-filter renderer wrapper under app/diff.
app/diff/exclude_test.go	Tests for exclude filter under app/diff.
app/diff/directory.go	Adds/moves all-files directory reader under app/diff.
app/diff/directory_test.go	Tests for directory reader under app/diff.
app/diff/diff.go	Adds/moves git diff renderer and unified diff parsing under app/diff.
app/diff/diff_test.go	Tests for git diff renderer and unified diff parsing under app/diff.
app/diff/blame.go	Adds/moves git blame support under app/diff.
app/diff/blame_test.go	Tests for blame parsing and behavior under app/diff.
app/annotation/store.go	Adds/moves annotation store under app/annotation.
app/annotation/store_test.go	Tests for annotation store under app/annotation.
.zed/tasks.json	Updates Zed run tasks to go run ./app ....
.goreleaser.yml	Updates GoReleaser build entry to main: ./app.
.claude-plugin/skills/revdiff/SKILL.md	Updates plugin skill install guidance (removes go install).
.claude-plugin/skills/revdiff/scripts/launch-revdiff.sh	Updates install hint to Homebrew/releases instead of go install.
.claude-plugin/skills/revdiff/references/install.md	Removes go install from plugin install reference.

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[Copilot]

make build writes the output binary to .bin/revdiff.$(BRANCH) but the .bin/ directory is not created anywhere in the Makefile. In a clean checkout this target will fail with “no such file or directory”. Consider adding a mkdir -p .bin step (or using $(shell mkdir -p .bin) via a dedicated prerequisite) before go build/cp.

Suggested change

	build:
	build:
	mkdir -p .bin