feat(rules): richer conditions — amount tolerance + date-part fields (P1)

[canalesb93]

Base: feat/rules-substrate. Implements P1 — richer rule conditions (roadmap §4a) of the rules-as-universal-substrate sprint. This is the condition expressiveness that lets agents encode recurrence as durable rules on raw + stable fields — subscriptions matched without a shipped detector.

What this adds

Amount tolerance operators on every numeric field:

• approx — value ± tolerance ({"field":"amount","op":"approx","value":15.49,"tolerance":0.5})
• between — inclusive min/max ({"field":"day_of_month","op":"between","min":1,"max":5})

Date-part fields, numeric, derived from the tz-naive date column (no timezone math — provider-localized): day_of_month, month, day_of_week (0=Sun), day_of_year. Support eq/range/between/approx.

day_of_month approx is cyclic (the 1st and the month's last day are 1 apart) and clamped (a target past a short month collapses to its last day, so "the 31st" matches Feb 28 / Feb 29 in a leap year). Boundary behavior uses each transaction's own month length, so the same rule is correct across every month and leap years.

Guidance (docs + MCP schema): express annual cadence as month = M AND day_of_month ≈ D ± N (leap-robust), never day_of_year (drifts ±1 after Feb).

The canonical recurrence rule is now expressible:

{ "and": [
  { "field": "amount", "op": "approx", "value": 15.49, "tolerance": 0.50 },
  { "field": "day_of_month", "op": "approx", "value": 14, "tolerance": 3 }
] }

Layers touched (complete system — mirrors #1874/#1876 metadata pattern)

Layer	Files
Service validation	internal/service/rules.go — validConditionFields (+4 date-parts), numericOps (+approx/between), per-op validation (tolerance ≥ 0, min ≤ max), CompiledCondition params, types.go Condition + TransactionContext.Date
Sync evaluation	internal/sync/rule_resolver.go — Condition/compiledCondition params, TransactionContext.Date, date-part evaluateLeaf cases, approx/between in evaluateNumeric, cyclic/clamped evaluateDayOfMonth; internal/sync/engine.go seeds tctx.Date = txn.Date
Retroactive + preview	internal/service/rules.go — added t.date to transactionContextQuery SELECT + GROUP BY, columns 15→16, row scan + finalize, and the preview query populates tctx.Date (so the new fields work in preview_rule and retroactive apply)
MCP	internal/mcp/tools.go — condition jsonschema updated with the new fields/ops + cyclic/annual guidance
Admin UI	internal/templates/components/pages/rule_form.templ (Date optgroup, ≈ ± + between ops, tolerance/min/max inputs) + static/js/admin/components/rule_form.js (fieldTypes, operator options, serialize/parse of tolerance/min/max)
Docs	docs/rule-dsl.md (fields + ops tables, match-stability stable-derived class, new "Amount tolerance" + "Date-part conditions" sections), docs/mcp-tools-reference.md

openapi.yaml unchanged: rule conditions are additionalProperties: true and no routes were added — TestOpenAPIDrift passes (same as the metadata PR #1874).

Evidence

Build / vet / unit (all green):

go build ./...        → ok
go vet ./...          → ok (incl. -tags integration)
go test ./internal/service/... ./internal/sync/... ./internal/mcp/...  → ok

The only failing unit test in the full go test ./... run was internal/agent's TestSidecarRun_ConcurrentRunsNoLongerSerialize — a pre-existing timing-flaky test unrelated to this change; it passed on re-run.

Integration (local Postgres):

DATABASE_URL=…/breadbox_test go test -tags integration -p 1 \
  ./internal/service/... ./internal/sync/... ./internal/db/...  → ok (all)
go test -tags integration -run TestOpenAPIDrift ./internal/api/... → ok

New tests:

• rules_dateparts_test.go / rule_resolver_dateparts_test.go — operator + date-part eval, cyclic/clamped day_of_month (Feb / 30- / 31-day / leap boundaries), composition.
• rules_dateparts_integration_test.go (service) — recurrence rule (amount approx X±Y AND day_of_month approx D±N → add_tag) and between+month rule via retroactive apply; only in-window charges tagged.
• rules_dateparts_integration_test.go (sync) — same recurrence rule fires during a real sync; only the in-window charge tagged.

UI — the rule-form builder showing the new ≈ ± operator with a tolerance input, the Day of month date-part field, and the between min–max inputs:

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