fix(db): exclude kind:30179 ciphertext from brownfield FTS (#6822)

## Problem

Kind `30179` (NIP-PMA private managed agent — NIP-44 ciphertext carrying
the agent nsec, env vars, prompt) joined `AUTHOR_ONLY_KINDS` in #4593,
but only **fresh** installs stopped indexing it:

- `migrations/0008` installs the positive FTS allowlist only when
`events` is empty;
- `migrations/0014` wraps the retained brownfield expression for `30350`
alone;
- `schema/schema.sql` still carries the legacy negative skip-set without
`30179`.

So a relay upgraded in place keeps tokenizing `30179` ciphertext into
`events.search_tsv`. Found by Wren while reviewing #4999 (which
activates publication of 30179 from Desktop). No readable leak: `/query`
applies `search_hit_accepted` + `event_visible_to_reader` before
serialization and live foreign searches against builderlab returned `[]`
— this is the storage-layer privacy invariant (`docs/nips/NIP-PMA.md`
deployment step 2) plus wasted FTS work.

## Fix

- `migrations/0033_private_managed_agent_fts.sql` — same shape as 0014:
capture the current generated expression via `pg_get_expr`, drop/re-add
`search_tsv` wrapped with `kind = 30179 → NULL`. Every other kind keeps
whatever policy the database already had (fresh allowlist or brownfield
skip-set). Rebuilds the GIN index; no heap-wide policy rewrite.
- `schema/schema.sql` — add `30179` to the desired-state skip-set.

## Tests

- `populated_upgrade_preserves_search_policy_except_for_private_kinds`
(renamed from `…_push_leases`): provisions the **legacy negative
expression** (migrations 1–7), inserts kind 1 / 30179 / 30350 rows,
checkpoints after 0014 (30179 still searchable, 30350 not), then runs to
head and asserts 30179 is NULL. **Proven red** with the 0033 file
removed: `left: [(1, Some(true)), (30179, Some(true)), (30350, None)]`.
- `embedded_migrator_contains_consolidated_initial_schema`: count 32→33,
asserts 0033 shape and `schema.sql` parity.
- `buzz-search/tests/fts_integration.rs` setup applies 0033 so the FTS
tripwires run against the real chain.

## Verification (HEAD 6154cc33d, same shell)

- `cargo test -p buzz-db -- --include-ignored --test-threads=1`: 305
passed / 3 failed — the 3
(`create_community_with_owner_enforces_per_owner_limit`,
`insert_mentions_indexes_rosters_past_bind_parameter_cap`,
`transfer_ownership_returns_limit_reached_for_maxed_transferee`) fail
identically on pristine `main` f24971033 with a fresh DB; unrelated to
this diff.
- `cargo test -p buzz-search -- --include-ignored`: 19 passed (incl.
`author_only_kinds_are_storage_level_unsearchable`,
`p_gated_persistent_kinds_have_storage_null_tsvector`).
- `desired_state_schema_bootstrap_progresses_beyond_fencing` +
`run_migrations_applies_consolidated_initial_schema_on_fresh_database`:
pass.
- `cargo fmt --all --check` clean; `cargo clippy -p buzz-db -p
buzz-search --all-targets -D warnings` clean.

Independent of #4999 — both main and #4999 are brownfield-exposed today;
this lands either order.

---------

Signed-off-by: Meli <5aaa86bce934fc3445fc254aab560a40923f10252f92107e665073dede0e04d3@buzz.block.builderlab.xyz>
Signed-off-by: Eva <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Co-authored-by: Meli <5aaa86bce934fc3445fc254aab560a40923f10252f92107e665073dede0e04d3@buzz.block.builderlab.xyz>
Co-authored-by: Eva <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>

schema/schema.sql

@@ -219,9 +219,9 @@ CREATE TABLE events (
     -- Privacy: encrypted/private routing wrappers and p-gated membership notices
     -- must never be discoverable through NIP-50 full-text search. NULL tsvector
     -- never matches `@@`.
-    -- Keep in sync with migrations (final state: 0001 + 0005 + 0009).
+    -- Keep in sync with migrations (final state: 0001 + 0005 + 0014 + 0033).
     search_tsv  TSVECTOR GENERATED ALWAYS AS (
-        CASE WHEN kind IN (1059, 30300, 30350, 30622, 44100, 44101, 44200) THEN NULL::tsvector
+        CASE WHEN kind IN (1059, 30179, 30300, 30350, 30622, 44100, 44101, 44200) THEN NULL::tsvector
              ELSE to_tsvector('simple', content)
         END
     ) STORED,