Extract normalizeLabels to shared utility package

The `normalizeLabels` function appears in multiple locations with identical implementation. Extract to a shared utility package.

Current locations:
- `internal/rpc/server.go:37` (53 lines) - full implementation
- `cmd/bd/list.go:50-52` - uses the server version (needs to use new shared version)

Function purpose:
- Trims whitespace from labels
- Removes empty strings
- Deduplicates labels
- Preserves order

Target structure:
```
internal/util/
├── strings.go         # String utilities
    └── NormalizeLabels([]string) []string
```

Impact: DRY principle, single source of truth, easier to test

- Create `internal/util/strings.go` with `NormalizeLabels`
- Add comprehensive unit tests in `internal/util/strings_test.go`
- Update `internal/rpc/server.go` to import and use `util.NormalizeLabels`
- Update `cmd/bd/list.go` to import and use `util.NormalizeLabels`
- Remove duplicate implementations
- All tests pass: `go test ./...`
- Verify label normalization works: test `bd list --label` commands


Extract SQLite migrations into separate files

The file `internal/storage/sqlite/sqlite.go` is 2,136 lines and contains 11 sequential migrations alongside core storage logic. Extract migrations into a versioned system.

Current issues:
- 11 migration functions mixed with core logic
- Hard to see migration history
- Sequential migrations slow database open
- No clear migration versioning

Migration functions to extract:
- `migrateDirtyIssuesTable()`
- `migrateIssueCountersTable()`
- `migrateExternalRefColumn()`
- `migrateCompositeIndexes()`
- `migrateClosedAtConstraint()`
- `migrateCompactionColumns()`
- `migrateSnapshotsTable()`
- `migrateCompactionConfig()`
- `migrateCompactedAtCommitColumn()`
- `migrateExportHashesTable()`
- Plus 1 more (11 total)

Target structure:
```
internal/storage/sqlite/
├── sqlite.go          # Core storage (~800 lines)
├── schema.go          # Table definitions (~200 lines)
├── migrations.go      # Migration orchestration (~200 lines)
└── migrations/        # Individual migrations
    ├── 001_initial_schema.go
    ├── 002_dirty_issues.go
    ├── 003_issue_counters.go
    [... through 011_export_hashes.go]
```

Benefits:
- Clear migration history
- Each migration self-contained
- Easier to review migration changes in PRs
- Future migrations easier to add

- All 11 migrations extracted to separate files
- Migration version tracking in database
- Migrations run in order on fresh database
- Existing databases upgrade correctly
- All tests pass: `go test ./internal/storage/sqlite/...`
- Database initialization time unchanged or improved
- Add migration rollback capability (optional, nice-to-have)


Remove unreachable utility functions

Several small utility functions are unreachable:

Files to clean:
1. `internal/storage/sqlite/hash.go` - `computeIssueContentHash` (line 17)
   - Check if entire file can be deleted if only contains this function

2. `internal/config/config.go` - `FileUsed` (line 151)
   - Delete unused config helper

3. `cmd/bd/git_sync_test.go` - `verifyIssueOpen` (line 300)
   - Delete dead test helper

4. `internal/compact/haiku.go` - `HaikuClient.SummarizeTier2` (line 81)
   - Tier 2 summarization not implemented
   - Options: implement feature OR delete method

Impact: Removes 50-100 LOC depending on decisions

- Remove unreachable functions
- If entire files can be deleted (like hash.go), delete them
- For SummarizeTier2: decide to implement or delete, document decision
- All tests pass: `go test ./...`
- Verify no callers exist for each function


Remove unreachable RPC methods

Several RPC server and client methods are unreachable and should be removed:

Server methods (internal/rpc/server.go):
- `Server.GetLastImportTime` (line 2116)
- `Server.SetLastImportTime` (line 2123)
- `Server.findJSONLPath` (line 2255)

Client methods (internal/rpc/client.go):
- `Client.Import` (line 311) - RPC import not used (daemon uses autoimport)

Evidence:
```bash
go run golang.org/x/tools/cmd/deadcode@latest -test ./...
```

Impact: Removes ~80 LOC of unused RPC code

- Remove the 4 unreachable methods (~80 LOC total)
- Verify no callers: `grep -r "GetLastImportTime\|SetLastImportTime\|findJSONLPath" .`
- All tests pass: `go test ./internal/rpc/...`
- Daemon functionality works: test daemon start/stop/operations


Refactor sqlite.go (2298 lines)

Break down internal/storage/sqlite/sqlite.go into smaller, more focused modules. The file is currently 2298 lines and should be split into logical components.


Wrap git operations in GitClient interface

Create internal/daemonrunner/git.go with GitClient interface (HasUpstream, HasChanges, Commit, Push, Pull). Default implementation using os/exec. Use in Syncer and Run loop for testability.


Document bd edit command and verify MCP exclusion

Follow-up from PR #152:
1. Add "bd edit" to AGENTS.md with "Humans only" note
2. Verify MCP server doesn't expose bd edit command
3. Consider adding test for command registration