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/graph.md

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+# Entity Relationship Explorer
+
+- **Command:** `lore graph <entity-type> <iid>`
+- **Confidence:** 80%
+- **Tier:** 3
+- **Status:** proposed
+- **Effort:** medium — BFS traversal (similar to timeline expand), output formatting
+
+## What
+
+Given an issue or MR, traverse `entity_references` and display all connected
+entities with relationship types and depths. Output as tree, JSON, or Mermaid diagram.
+
+## Why
+
+The entity_references graph is already built (Gate 2) but has no dedicated
+exploration command. Timeline shows events over time; this shows the relationship
+structure. "What's connected to this issue?" is a different question from "what
+happened to this issue?"
+
+## Data Required
+
+All exists today:
+- `entity_references` (source/target entity, reference_type)
+- `issues` / `merge_requests` (for entity context)
+- Timeline expand stage already implements BFS over this graph
+
+## Implementation Sketch
+
+```
+1. Resolve entity type + iid to local ID
+2. BFS over entity_references:
+   - Follow source→target AND target→source (bidirectional)
+   - Track depth (--depth flag, default 2)
+   - Track reference_type for edge labels
+3. Hydrate each discovered entity with title, state, URL
+4. Format as tree / JSON / Mermaid
+```
+
+## Human Output (Tree)
+
+```
+#42 Login timeout bug (CLOSED)
+  ├── closes ── !234 Refactor auth middleware (MERGED)
+  │   ├── mentioned ── #38 Connection timeout in auth flow (CLOSED)
+  │   └── mentioned ── #51 Token refresh improvements (OPEN)
+  ├── related ── #45 Auth module documentation (OPEN)
+  └── mentioned ── !228 Database migration (MERGED)
+      └── closes ── #35 Schema version drift (CLOSED)
+```
+
+## Mermaid Output
+
+```mermaid
+graph LR
+    I42["#42 Login timeout"] -->|closes| MR234["!234 Refactor auth"]
+    MR234 -->|mentioned| I38["#38 Connection timeout"]
+    MR234 -->|mentioned| I51["#51 Token refresh"]
+    I42 -->|related| I45["#45 Auth docs"]
+    I42 -->|mentioned| MR228["!228 DB migration"]
+    MR228 -->|closes| I35["#35 Schema drift"]
+```
+
+## Downsides
+
+- Overlaps somewhat with timeline (but different focus: structure vs chronology)
+- High fan-out for popular entities (need depth + limit controls)
+- Unresolved cross-project references appear as dead ends
+
+## Extensions
+
+- `lore graph --format dot` — GraphViz DOT output
+- `lore graph --format mermaid` — Mermaid diagram
+- `lore graph --include-discussions` — show discussion threads as nodes
+- Interactive HTML visualization (future web UI)