chore(welcome): replace vague "tracked separately" claim with explicit FIXME anchor

v0.9.5 review — PM P2. The comment at `welcome.ts:46` referenced a
"pre-existing telemetry-init gap (tracked separately)" — a claim that
implied a tracking issue existed. It didn't (verified by searching open
issues on `AltimateAI/altimate-code`).

Rewritten to:
- Anchor the gap with `FIXME(telemetry-init-config-opt-out)` so it shows
  up in code searches.
- Describe the exact failure mode: `doInit()` may run before
  `Instance.provide()` has made `Config.get()` resolvable — the catch
  branch in `telemetry/index.ts::doInit` proceeds with telemetry enabled,
  so a user who opted out via `telemetry.disabled` config (env var not
  set) can still have a machine-id minted on cold-start.
- Explicitly note the env-var opt-out
  (`ALTIMATE_TELEMETRY_DISABLED` / `OPENCODE_DISABLE_TELEMETRY`) is
  unaffected — that check doesn't need Instance context.
- Honestly state no tracking issue currently exists rather than repeat
  the earlier false claim.

Pre-existing (not introduced by this release). Filed as part of the
release/v0.9.5 deferred-items tracker.

Author: sahrizvi

packages/opencode/src/cli/welcome.ts

@@ -43,10 +43,16 @@ export function showWelcomeBannerIfNeeded(): void {
     // launch. Probe existence with existsSync only — do NOT mint here. Minting is left to
     // Telemetry.doInit() (its job, not the welcome banner's); the first_launch machine_id is
     // attached at flush time from telemetry module state, so it does not depend on minting here.
-    // NOTE: doInit's early call runs before an Instance is available, so its CONFIG opt-out gate
-    // fails open and it can still mint for a config-only opt-out user. That is a pre-existing
-    // telemetry-init gap (tracked separately), not something this banner can fix — this code just
-    // stops adding a SECOND minting site under an even weaker (env-only) gate.
+    //
+    // FIXME(telemetry-init-config-opt-out): doInit() may run before Instance.provide() has made
+    // Config.get() resolvable (see the try/catch around Config.get in telemetry/index.ts::doInit
+    // — the catch branch proceeds with telemetry enabled). A user who opted out via the
+    // `telemetry.disabled` config key — with no env var set — can therefore still get a
+    // machine-id minted on first launch. The env-var opt-out (ALTIMATE_TELEMETRY_DISABLED /
+    // OPENCODE_DISABLE_TELEMETRY) is unaffected — that check does not need Instance context.
+    // Pre-existing (not introduced by this release); calling it out explicitly here rather than
+    // leaving the earlier "(tracked separately)" wording, which claimed a tracking issue that
+    // does not currently exist.
     const machineIdPath = path.join(os.homedir(), ".altimate", "machine-id")
     const isUpgrade = fs.existsSync(machineIdPath)
     // altimate_change end