fix: check cwd for .beads/ before git-worktree resolution

[julianknutsen]

Summary

When a subdirectory has its own .beads/ inside a git worktree that also has .beads/ at its root, the git-worktree check (step 2b in FindBeadsDir) finds the root's .beads/ before the cwd walk (step 3) can discover the local one.

This causes incorrect database connections when orchestrators like Gas City manage multiple "rigs" (project subdirectories) that each have their own beads database, nested inside a parent git repo that also tracks beads.

Problem

Reproduction scenario:

/project/                    ← git worktree root
├── .beads/                  ← project's beads (prefix: mc, port: 49880)
│   ├── config.yaml
│   └── metadata.json
└── rig-a/                   ← orchestrator-managed rig
    └── .beads/              ← rig's beads (prefix: tr, port: 46345)
        ├── config.yaml
        └── metadata.json

When bd list runs from rig-a/, it should connect to tr on port 46345. Instead, FindBeadsDir() returns /project/.beads/ (the git root's), connecting to the wrong database.

Root cause: FindBeadsDir() step 2b checks git.GetRepoRoot() for .beads/ before step 3 walks up from cwd. Since git.GetRepoRoot() returns /project/ (the worktree toplevel), it finds the root's .beads/ first. The same issue exists in findDatabaseInTree() which is used by FindDatabasePath().

Fix

Add a cwd check before git-worktree resolution in both FindBeadsDir() and findDatabaseInTree(). If cwd has a valid .beads/ directory (with project files or a database), return it immediately.

Priority order is now:

1. BEADS_DIR env var (unchanged)
2. cwd .beads/ (NEW — most-local directory wins)
3. Git worktree root .beads/ (unchanged)
4. Walk up from cwd (unchanged)

Tests

6 new tests in internal/beads/cwd_priority_test.go:

Test	Scenario
TestFindBeadsDir_CwdPriority	Rig .beads/ wins over git root .beads/
TestFindDatabasePath_CwdPriority	Same for database path discovery
TestFindBeadsDir_CwdWithoutBeads_FallsBackToWalk	Normal walk-up when cwd has no .beads/
TestFindBeadsDir_CwdBeadsDirWithRedirect	Redirect in cwd .beads/ is followed
TestFindBeadsDir_BEADS_DIR_StillTakesPriority	BEADS_DIR env still wins over cwd
TestFindBeadsDir_CwdEmptyBeadsDir_SkipsToCwdWalk	Empty .beads/ dir (no project files) skipped

All existing tests continue to pass.

Backward Compatibility

This change only affects users who have nested .beads/ directories inside a git worktree — a scenario specific to multi-rig orchestration. Single-project repos, worktrees, and redirects are unaffected because the cwd check only fires when cwd literally contains .beads/ with valid project files.