docs: add feature ideas catalog, time-decay scoring plan, and timeline issue doc

Ideas catalog (docs/ideas/): 25 feature concept documents covering future
lore capabilities including bottleneck detection, churn analysis, expert
scoring, collaboration patterns, milestone risk, knowledge silos, and more.
Each doc includes motivation, implementation sketch, data requirements, and
dependencies on existing infrastructure. README.md provides an overview and
SYSTEM-PROPOSAL.md presents the unified analytics vision.

Plans (plans/): Time-decay expert scoring design with four rounds of review
feedback exploring decay functions, scoring algebra, and integration points
with the existing who-expert pipeline.

Issue doc (docs/issues/001): Documents the timeline pipeline bug where
EntityRef was missing project context, causing ambiguous cross-project
references during the EXPAND stage.

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

docs/ideas/stale-discussions.md

@@ -0,0 +1,100 @@
+# Stale Discussion Finder
+
+- **Command:** `lore stale-discussions [--days <N>]`
+- **Confidence:** 90%
+- **Tier:** 1
+- **Status:** proposed
+- **Effort:** low — single query, minimal formatting
+
+## What
+
+List unresolved, resolvable discussions where `last_note_at` is older than a
+threshold (default 14 days), grouped by parent entity. Prioritize by discussion
+count per entity (more stale threads = more urgent).
+
+## Why
+
+Unresolved discussions are silent blockers. They prevent MR merges, stall
+decision-making, and represent forgotten conversations. This surfaces them so teams
+can take action: resolve, respond, or explicitly mark as won't-fix.
+
+## Data Required
+
+All exists today:
+- `discussions` (resolved, resolvable, last_note_at)
+- `issues` / `merge_requests` (for parent entity context)
+
+## Implementation Sketch
+
+```sql
+SELECT
+    d.id,
+    d.noteable_type,
+    CASE WHEN d.issue_id IS NOT NULL THEN i.iid ELSE mr.iid END as entity_iid,
+    CASE WHEN d.issue_id IS NOT NULL THEN i.title ELSE mr.title END as entity_title,
+    p.path_with_namespace,
+    d.last_note_at,
+    ((?1 - d.last_note_at) / 86400000) as days_stale,
+    COUNT(*) OVER (PARTITION BY COALESCE(d.issue_id, d.merge_request_id), d.noteable_type) as stale_count_for_entity
+FROM discussions d
+JOIN projects p ON d.project_id = p.id
+LEFT JOIN issues i ON d.issue_id = i.id
+LEFT JOIN merge_requests mr ON d.merge_request_id = mr.id
+WHERE d.resolved = 0
+  AND d.resolvable = 1
+  AND d.last_note_at < ?1
+ORDER BY days_stale DESC;
+```
+
+## Human Output Format
+
+```
+Stale Discussions (14+ days without activity)
+
+group/backend !234 — Refactor auth middleware (3 stale threads)
+  Discussion #a1b2c3  (28d stale)  "Should we use JWT or session tokens?"
+  Discussion #d4e5f6  (21d stale)  "Error handling for expired tokens"
+  Discussion #g7h8i9  (14d stale)  "Performance implications of per-request validation"
+
+group/backend #90 — Rate limiting design (1 stale thread)
+  Discussion #j0k1l2  (18d stale)  "Redis vs in-memory rate counter"
+```
+
+## Robot Mode Output
+
+```json
+{
+  "ok": true,
+  "data": {
+    "threshold_days": 14,
+    "total_stale": 4,
+    "entities": [
+      {
+        "type": "merge_request",
+        "iid": 234,
+        "title": "Refactor auth middleware",
+        "project": "group/backend",
+        "stale_discussions": [
+          {
+            "discussion_id": "a1b2c3",
+            "days_stale": 28,
+            "first_note_preview": "Should we use JWT or session tokens?"
+          }
+        ]
+      }
+    ]
+  }
+}
+```
+
+## Downsides
+
+- Some discussions are intentionally left open (design docs, long-running threads)
+- Could produce noise in repos with loose discussion hygiene
+- Doesn't distinguish "stale and blocking" from "stale and irrelevant"
+
+## Extensions
+
+- `lore stale-discussions --mr-only` — focus on MR review threads (most actionable)
+- `lore stale-discussions --author alice` — "threads I started that went quiet"
+- `lore stale-discussions --assignee bob` — "threads on my MRs that need attention"