feat(bd-226s): implement time-decay expert scoring model

Replace flat-weight expertise scoring with exponential half-life decay,
split reviewer signals (participated vs assigned-only), dual-path rename
awareness, and new CLI flags (--as-of, --explain-score, --include-bots,
--all-history).

Changes:
- ScoringConfig: 8 new fields with validation (config.rs)
- half_life_decay() and normalize_query_path() pure functions (who.rs)
- CTE-based SQL with dual-path matching, mr_activity, reviewer_participation (who.rs)
- Rust-side decay aggregation with deterministic f64 ordering (who.rs)
- Path resolution probes check old_path columns (who.rs)
- Migration 026: 5 new indexes for dual-path and reviewer participation
- Default --since changed from 6m to 24m
- 31 new tests (example-based + invariant), 621 total who tests passing
- Autocorrect registry updated with new flags

Closes: bd-226s, bd-2w1p, bd-1soz, bd-18dn, bd-2ao4, bd-2yu5, bd-1b50,
bd-1hoq, bd-1h3f, bd-13q8, bd-11mg, bd-1vti, bd-1j5o

src/cli/mod.rs

@@ -910,6 +910,26 @@ pub struct WhoArgs {
 
     #[arg(long = "no-detail", hide = true, overrides_with = "detail")]
     pub no_detail: bool,
+
+    /// Score as if "now" is this date (ISO 8601 or duration like 30d). Expert mode only.
+    #[arg(long = "as-of", help_heading = "Scoring")]
+    pub as_of: Option<String>,
+
+    /// Show per-component score breakdown in output. Expert mode only.
+    #[arg(long = "explain-score", help_heading = "Scoring")]
+    pub explain_score: bool,
+
+    /// Include bot users in results (normally excluded via scoring.excluded_usernames).
+    #[arg(long = "include-bots", help_heading = "Scoring")]
+    pub include_bots: bool,
+
+    /// Remove the default time window (query all history). Conflicts with --since.
+    #[arg(
+        long = "all-history",
+        help_heading = "Filters",
+        conflicts_with = "since"
+    )]
+    pub all_history: bool,
 }
 
 #[derive(Parser)]