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/decisions.md

@@ -0,0 +1,94 @@
+# Decision Archaeology
+
+- **Command:** `lore decisions <query>`
+- **Confidence:** 82%
+- **Tier:** 2
+- **Status:** proposed
+- **Effort:** medium — search pipeline + regex pattern matching on notes
+
+## What
+
+Search for discussion notes that contain decision-making language. Use the existing
+search pipeline but boost notes containing patterns like "decided", "agreed",
+"will go with", "tradeoff", "because we", "rationale", "the approach is", "we chose".
+Return the surrounding discussion context.
+
+## Why
+
+This is gitlore's unique value proposition — "why was this decision made?" is the
+question that no other tool answers well. Architecture Decision Records are rarely
+maintained; the real decisions live in discussion threads. This mines them.
+
+## Data Required
+
+All exists today:
+- `documents` + search pipeline (for finding relevant entities)
+- `notes` (body text for pattern matching)
+- `discussions` (for thread context)
+
+## Implementation Sketch
+
+```
+1. Run existing hybrid search to find entities matching the query topic
+2. For each result entity, query all discussion notes
+3. Score each note against decision-language patterns:
+   - Strong signals (weight 3): "decided to", "agreed on", "the decision is",
+     "we will go with", "approved approach"
+   - Medium signals (weight 2): "tradeoff", "because", "rationale", "chosen",
+     "opted for", "rejected", "alternative"
+   - Weak signals (weight 1): "should we", "proposal", "option A", "option B",
+     "pros and cons"
+4. Return notes scoring above threshold, with surrounding context (previous and
+   next note in discussion thread)
+5. Sort by: search relevance * decision score
+```
+
+### Decision Patterns (regex)
+
+```rust
+const STRONG_PATTERNS: &[&str] = &[
+    r"(?i)\b(decided|agreed|approved)\s+(to|on|that)\b",
+    r"(?i)\bthe\s+(decision|approach|plan)\s+is\b",
+    r"(?i)\bwe('ll| will| are going to)\s+(go with|use|implement)\b",
+    r"(?i)\blet'?s\s+(go with|use|do)\b",
+];
+
+const MEDIUM_PATTERNS: &[&str] = &[
+    r"(?i)\b(tradeoff|trade-off|rationale|because we|opted for)\b",
+    r"(?i)\b(rejected|ruled out|won't work|not viable)\b",
+    r"(?i)\b(chosen|selected|picked)\b.{0,20}\b(over|instead of)\b",
+];
+```
+
+## Human Output
+
+```
+Decisions related to "authentication"
+
+group/backend !234 — "Refactor auth middleware"
+  Discussion #a1b2c3 (alice, 3w ago):
+    "We decided to use JWT with short-lived tokens instead of session cookies.
+     The tradeoff is more complexity in the refresh flow, but we get stateless
+     auth which scales better."
+    Decision confidence: HIGH (3 strong pattern matches)
+
+group/backend #42 — "Auth architecture review"
+  Discussion #d4e5f6 (bob, 2mo ago):
+    "After discussing with the security team, we'll go with bcrypt for password
+     hashing. Argon2 is theoretically better but bcrypt has wider library support."
+    Decision confidence: HIGH (2 strong pattern matches)
+```
+
+## Downsides
+
+- Pattern matching is imperfect; may miss decisions phrased differently
+- May surface "discussion about deciding" rather than actual decisions
+- Non-English discussions won't match
+- Requires good search results as input (garbage in, garbage out)
+
+## Extensions
+
+- `lore decisions --recent` — decisions made in last 30 days
+- `lore decisions --author alice` — decisions made by specific person
+- Export as ADR (Architecture Decision Record) format
+- Combine with timeline for chronological decision history