feat(shell): open project_open across all of ~/Code

[codepuncher]

Stacked on #204 (base is po-autocomplete; will auto-retarget to master once #204 merges).

What

Generalises project_open/po and their bash/zsh completion from the single ~/Code/wordpress base to any project discovered anywhere under ~/Code. project_open HoldFast now opens ~/Code/mods/HoldFast.

• A "project" is the outermost dir containing .git, bedrock, or site; the walk stops there, so vendored submodules (lib/vcpkg, ...) are excluded.
• Existing WordPress behaviour preserved: bedrock/site descent, the theme target, and <subdir> second-arg navigation, all gated on markers.
• First-arg completion lists every discovered project; second-arg completion lists the resolved project's immediate subdirs.
• Discovery is backed by an on-disk cache ($XDG_CACHE_HOME/project_open/projects) rebuilt asynchronously at shell startup, so tab-completion never walks the tree. po_refresh forces a rebuild.

Notes

• All discovery helpers avoid <() process substitution: under zsh, a <() that calls a function nested inside $(...) empties $PATH, which broke cat/find in completion. Cache reads use shell builtins / here-strings; scans use pipes.
• No name-collision handling (basenames assumed unique across ~/Code, confirmed); no per-TAB freshness check; no new external dependency.

Testing

• tests/project_open_test.sh: 18 assertions (scan, cache + TTL guard, resolve, completion helpers, WordPress descent) pass under bash.
• Manual: verified end-to-end in interactive bash and zsh (resolve, projects, targets, cd, bedrock/site descent, not-found status, $PATH intact).
• shellcheck shell/aliases and zsh -n shell/aliases clean.

Design spec and implementation plan included under docs/superpowers/.

[Copilot]

Pull request overview

Generalizes project_open/po from a fixed ~/Code/wordpress base to discovering and opening projects anywhere under ~/Code, backed by an on-disk cache so completion stays fast.

Changes:

• Add recursive project discovery (.git, bedrock, site) and name resolution with a cached index under $XDG_CACHE_HOME.
• Update project_open to resolve by basename and preserve existing WordPress-specific descent behavior.
• Add a standalone bash test script covering scan/cache/resolve/completion helpers and project_open runtime behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
shell/aliases	Adds project discovery + cache helpers, switches project_open to resolve projects across ~/Code, and triggers async cache rebuild on shell startup.
tests/project_open_test.sh	New standalone fixture-based tests for discovery, cache TTL behavior, resolution, completion helper output, and project_open navigation.
docs/superpowers/specs/2026-06-23-project-open-code-wide-design.md	Design spec describing discovery markers, caching strategy, and completion behavior.
docs/superpowers/plans/2026-06-23-project-open-code-wide.md	Implementation plan documenting step-by-step changes and testing strategy.

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