feat(mcp): add get_domain_summary() for low-token domain session orientation

get_state_summary() returns ~10k tokens — too expensive for routine domain
repo sessions that only need their own workstreams and decisions.

New get_domain_summary(domain_slug):
- 5 targeted API calls: topics (filter), workstreams (topic+status), decisions
  (topic+pending), progress (topic, limit 5), repos (domain, slug+SBOM only)
- Returns: topic, active workstreams, blocking decisions, 5 recent events,
  repo SBOM status — all scoped to one domain
- Estimated ~80-90% token reduction vs get_state_summary()

get_state_summary() preserved unchanged for cross-domain / custodian sessions.
Updated its docstring to note the large response and point to get_domain_summary.

Template updated: Step 1 now calls get_domain_summary("{DOMAIN}") instead of
get_state_summary() + get_next_steps(). TOOLS.md updated with usage guidance.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/project_claude_md.template

@@ -17,8 +17,7 @@ this orientation sequence. Do not greet, do not ask what to do first.**
 
 **Step 1 — Call the State Hub**
 ```
-get_state_summary()   # orientation: workstreams, decisions, recent progress
-get_next_steps()      # contextual suggestions from resolved decisions
+get_domain_summary("{DOMAIN}")   # workstreams, blocking decisions, recent progress, SBOM status
 ```
 If the call fails, the API is offline: `cd ~/the-custodian/state-hub && make api`