feat: add .recur app bundles (install, pack, startup auto-register)

[directedbits]

Summary

Adds app bundles: a .recur zip archive containing a recurfile (the single YAML file at its root) plus any local scripts an app needs, so an app travels as one file. Installing unpacks the bundle into ~/.config/recur/app/<name>/ and registers its recurfile; apps installed while the daemon is stopped are auto-registered on next start.

This is Part 1 of a two-part effort. The optional bundle dependency check (Part 2) is intentionally deferred pending a decision on approach, and nothing here depends on it.

• Are new tests required? (added — unit + manual e2e)
• Does documentation need to be updated? (user docs + requirements spec added in this PR)
• Contains breaking changes?
• Touches plugin contract, manifest format, or recurfile YAML schema? (deliberately no schema change)
• Changes daemon config keys or plugin options?
• Affects daemon startup/shutdown behavior? (startup app-folder scan)
• Changes CLI flags or command signatures? (new recur app subcommands)

Changes

• appbundle package (src/infra/fs/appbundle/): traversal-safe zip pack/unpack preserving layout and file modes; relaxed root-YAML recurfile selection (any single root YAML is the recurfile; a conventional recurfile.* breaks ties when several are present).
• recur app install <bundle.recur | URL>: resolves the source (URL downloads reuse the plugin path's allowed_hosts gate), unpacks via a staging dir so a bad bundle never clobbers an installed app, derives the name (recurfile stem → bundle stem, --name overrides), prompts overwrite/abandon on collision (--force to skip), then registers with the daemon. Daemon-down installs just unpack and defer registration.
• recur app list / remove / pack: the rest of the lifecycle, incl. an authoring command to build bundles.
• Daemon startup scan (scanAppFolder, hooked into Run() after state replay): registers apps under ~/.config/recur/app/ not already registered, idempotent via new registry.hasRecurfilePath.
• configyaml.AppDir(): single source of truth for the app directory path, shared by CLI and daemon.
• Docs & spec: requirements/app-bundles.md (spec + acceptance criteria), recur app commands added to requirements/cli-commands.md, startup scan noted in requirements/daemon-lifecycle.md, a user guide at docs/content/docs/configuration/app-bundles.md, and a CLI reference section.

Test plan

• Unit tests pass (task test) — new tests for bundle round-trip/mode-preservation/traversal/selection, CLI install/name-resolution/overwrite-abort/force/list/remove/pack, and daemon scan register/idempotent/skip-non-app.
• Plugin tests pass (task test:plugins) — n/a, no plugin changes.
• E2E tests pass (task test:e2e) — formal suite not run; manual e2e performed: installed a bundle with the daemon down → started the daemon → app auto-registered (app list shows "registered", daemon lists 1 group/1 trigger/1 action); list/remove/pack verified. task lint:go reports 0 issues.

Checklist

• Tests added or updated for new/changed behavior
• Spec in requirements/ updated — requirements/app-bundles.md plus cli-commands/daemon-lifecycle updates
• User docs updated — docs/content/docs/configuration/app-bundles.md and the CLI reference
• Small, buildable commits — feature + docs split into two commits, each compiles and passes tests
• No breaking changes — additive only

Breaking changes

None.

[github-actions]

Binary Size Report

Binary	Base	PR	Delta
recur	20MiB	20MiB	+110KiB
recurd	17MiB	17MiB	+12KiB