fix(costs): disable cost tracking until Claude Code exposes cost data

Cost tracking infrastructure works but has no data source:
- Claude Code displays costs in TUI status bar, not scrollback
- tmux capture-pane can't see TUI chrome
- All sessions show $0.00

Changes:
- Mark gt costs command as [DISABLED] with deprecation warnings
- Mark costs-digest patrol step as [DISABLED] with skip instructions
- Document requirement for Claude Code to expose CLAUDE_SESSION_COST

Infrastructure preserved for re-enabling when Claude Code adds support.

Ref: GH#24, gt-7awfjq

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/formula/formulas/mol-deacon-patrol.formula.toml

@@ -629,41 +629,29 @@ Skip dispatch - system is healthy.
 
 [[steps]]
 id = "costs-digest"
-title = "Aggregate daily costs"
+title = "Aggregate daily costs [DISABLED]"
 needs = ["session-gc"]
 description = """
-**DAILY DIGEST** - Aggregate yesterday's session cost wisps.
+**⚠️ DISABLED** - Skip this step entirely.
 
-Session costs are recorded as ephemeral wisps (not exported to JSONL) to avoid
-log-in-database pollution. This step aggregates them into a permanent daily
-"Cost Report YYYY-MM-DD" bead for audit purposes.
+Cost tracking is temporarily disabled because Claude Code does not expose
+session costs in a way that can be captured programmatically.
 
-**Step 1: Check if digest is needed**
-```bash
-# Preview yesterday's costs (dry run)
-gt costs digest --yesterday --dry-run
-```
+**Why disabled:**
+- The `gt costs` command uses tmux capture-pane to find costs
+- Claude Code displays costs in the TUI status bar, not in scrollback
+- All sessions show $0.00 because capture-pane can't see TUI chrome
+- The infrastructure is sound but has no data source
 
-If output shows "No session cost wisps found", skip to Step 3.
+**What we need from Claude Code:**
+- Stop hook env var (e.g., `$CLAUDE_SESSION_COST`)
+- Or queryable file/API endpoint
 
-**Step 2: Create the digest**
-```bash
-gt costs digest --yesterday
-```
+**Re-enable when:** Claude Code exposes cost data via API or environment.
 
-This:
-- Queries all session.ended wisps from yesterday
-- Creates a single "Cost Report YYYY-MM-DD" bead with aggregated data
-- Deletes the source wisps
+See: GH#24, gt-7awfj
 
-**Step 3: Verify**
-The digest appears in `gt costs --week` queries.
-Daily digests preserve audit trail without per-session pollution.
-
-**Timing**: Run once per morning patrol cycle. The --yesterday flag ensures
-we don't try to digest today's incomplete data.
-
-**Exit criteria:** Yesterday's costs digested (or no wisps to digest)."""
+**Exit criteria:** Skip this step - proceed to next."""
 
 [[steps]]
 id = "patrol-digest"