feat: LibriVox/NASA/Internet Archive fetchers (+ deferred stubs)

Per sub-project-2 plan Task 9 / spec §6.4. Three keyless first-ship fetchers
parse documented JSON APIs via an injected HttpClient; license/attribution go
through tools.licensing; NASA third-party + IA no-license cases are flagged in
notes for review. musopen/fma/freesound are explicit deferred stubs raising
NotImplementedError; freesound documents FREESOUND_API_TOKEN (secret, env-only).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/ingest/fma.py

@@ -0,0 +1,26 @@
+"""Free Music Archive fetcher — DEFERRED (see spec §6.4).
+
+CC-licensed music (cc_by / cc_by_nc / cc0). Highest API-stability risk: the
+public FMA API has been deprecated/changed, so a real implementation resolves
+from a track URL + page metadata. The Fetcher seam is wired; it raises until
+implemented.
+"""
+
+from __future__ import annotations
+
+from tools.ingest.base import Candidate
+
+_DEFERRED = "deferred — see spec §6.4 (FMA public API deprecated/changed)"
+
+
+class FmaFetcher:
+    archive = "fma"
+
+    def __init__(self, client):
+        self.client = client
+
+    def search(self, query: str, *, limit: int) -> list[Candidate]:
+        raise NotImplementedError(_DEFERRED)
+
+    def resolve(self, identifier: str) -> Candidate:
+        raise NotImplementedError(_DEFERRED)