chore(open-source): sanitize real infra identifiers; tighten .gitignore

Open-source readiness plan, Phase 1 items 3 and 5.

Item 3 turned out to be far narrower than the plan's "93 files" once each hit
was classified rather than bulk-replaced. Sanitized only genuine operator
identifiers:

- FIPS test fixtures and a pine_ha comment carried real node LAN addresses ->
  RFC 5737 TEST-NET-1, the convention already used elsewhere in this repo.
- Real tailnet addresses in fips/endpoints.rs, mock-backend.js and the mesh
  test runner -> the base of the CGNAT range, obviously synthetic.
- Incident comments in appgate/mod.rs and apps/fedimint/manifest.yml named a
  specific node; the role is what carries the meaning, so the address is gone.
- CHANGELOG.md held five real addresses in published release notes — the most
  exposed of the lot.

Deliberately NOT touched, because the plan's item-3 list is over-broad and
following it literally would break working code:

- 192.168.1.1 / .254, 192.168.0.0/16 and 100.64.0.0/10 are generic router
  defaults, RFC1918 classification in backup_rpc, and CGNAT range logic in
  pine_ha / CompanionIntroOverlay. Not leaked infra.
- `tx1138` is listed as a hostname to scrub but is two live things: the
  user-facing default block explorer (`DEFAULT_TX_EXPLORER`) and
  `RETIRED_TX1138_HOST`, the migration constant whose entire job is stripping
  that retired registry from existing nodes' saved mirror lists. Scrubbing
  either breaks a feature. The plan needs this correction.
- Android's `192.168.1.100` strings are UI placeholder text.

Item 5: added *.key, *.pem, id_rsa*, *.sqlite, *.db to .gitignore, with a
negation for core/archipelago/src/appgate/testdata/*.key. Checked those first —
they are documented throwaway TLS fixtures compiled in via include_bytes!, not
node identity — and the negation stops the new rule silently dropping them if
they are ever regenerated. Verified both directions: fixtures not ignored, a
stray key elsewhere caught.

Verified: residual grep for real infra addresses is clean; audit-secrets.sh
still 5/5; app-catalog drift 0 (the fedimint edit is a YAML comment, which does
not survive parsing into the signed catalog); 44/44 fips tests pass with the
rewritten assertion fixtures.

Note: these test runs shared the working tree with another agent's in-flight
LND work, which was present but unstaged and is not part of this commit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/archipelago/src/fips/anchors.rs

@@ -477,19 +477,19 @@ mod tests {
     fn lan_fips_anchors_builds_direct_entry() {
         let peer = crate::transport::PeerRecord {
             did: "did:key:zpeer".to_string(),
-            lan_address: Some("192.168.63.198:5678".to_string()),
+            lan_address: Some("192.0.2.198:5678".to_string()),
             fips_npub: Some("npub1peer".to_string()),
             ..Default::default()
         };
         let out = lan_fips_anchors(&[peer]);
         assert_eq!(out.len(), 1);
-        assert_eq!(out[0].address, format!("192.168.63.198:{FIPS_UDP_PORT}"));
+        assert_eq!(out[0].address, format!("192.0.2.198:{FIPS_UDP_PORT}"));
         assert_eq!(out[0].transport, "udp");
 
         // Peers missing either the LAN address or the npub produce nothing.
         let no_npub = crate::transport::PeerRecord {
             did: "did:key:zother".to_string(),
-            lan_address: Some("192.168.63.199:5678".to_string()),
+            lan_address: Some("192.0.2.199:5678".to_string()),
             ..Default::default()
         };
         assert!(lan_fips_anchors(&[no_npub]).is_empty());