Introduces event, goal, and task storage subsystems built on Badger:

- event: append-only log with typed payloads for state changes
- goal: CRUD operations for session goals with event tracking
- task: full lifecycle management with status indexing
- testutil: helpers for deterministic test clocks and databases
- timeutil: clock abstraction for testability

All packages include comprehensive test coverage.

Co-authored-by: Crush <crush@charm.land>

Fix View transaction to return nil on success instead of ctx.Err(),
which
caused spurious failures when a context deadline was set but the
operation
completed successfully before expiration.

Improve configuration defaults for CLI durability:
- Default SyncWrites to true to ensure planning state persists across
  crashes
- Use os.UserConfigDir() instead of custom platform logic for better
cross-platform config directory handling

Code cleanup:
- Remove redundant txn.Discard() after successful commit
- Rename suffixTasks to suffixTask for singular/plural consistency
- Fix KeyString doc to correctly state it allocates
- Remove unused ctx assignment in View

Signed-off-by: Crush <crush@charm.land>

Refine the Badger helpers.

Signed-off-by: Crush <crush@charm.land>

Co-authored-by: Crush <crush@charm.land>

Had a combo of Claude Code/Sonnet 4.5 and Amp/GPT-5 (Oracle) write one
schema each, then used CC and Crush/GPT-5 (high) to polish up CC's
version. Then I presented both schemas to CC and Crush/GPT-5 and asked
which they prefer. Both suggested copying some choice ideas from CC's
schema, but instead adopting Amp's schema overall.

Co-authored-by: Crush <crush@charm.land>

Co-authored-by: Crush <crush@charm.land>

A bit too buggy to use yet