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>

mcp_server/TOOLS.md

@@ -24,7 +24,8 @@ Do not use them as a substitute for formal work definition inside the domain rep
 
 | Tool | Key Args | When to use |
 |------|----------|-------------|
-| `get_state_summary()` | — | **Session start.** Full snapshot: totals, blocking decisions, blocked tasks, open workstreams, last 20 events. |
+| `get_domain_summary(domain_slug)` | `domain_slug`: e.g. `"railiance"` | **Domain session start.** Scoped snapshot: active workstreams, blocking decisions, last 5 events, repo SBOM status — ~10% of get_state_summary() token cost. |
+| `get_state_summary()` | — | **Cross-domain work / custodian sessions.** Full snapshot: totals, all blocking decisions, all blocked tasks, all open workstreams, last 20 events. Large (~10k tokens). |
 | `get_topic(slug)` | `slug`: e.g. `"markitect"` | Deep-dive on one topic + its workstreams + recent events. |
 | `list_blocked_tasks(workstream_id?)` | optional filter | Surface all impediments, optionally scoped to one workstream. |
 | `list_pending_decisions(topic_id?)` | optional filter | Decisions holding up work, sorted by deadline. |