fix: prevent duplicate path prefixes and consolidate shared file updates

PowerShell release script:
- Add deduplication pass to Rewrite-Paths function
- Prevents .specify.specify/ double prefixes in generated commands
- Matches bash script behavior with regex '(?:\.specify/){2,}' -> '.specify/'

Bash update-agent-context script:
- Consolidate AGENTS.md updates to single call
- Remove redundant calls for $AMP_FILE, $KIRO_FILE, $BOB_FILE, $FORGE_FILE
- Update label to 'Codex/opencode/Amp/Kiro/Bob/Pi/Forge' to reflect all agents
- Prevents always-deduped $FORGE_FILE call that never executed

Both fixes improve efficiency and correctness while maintaining parity
between bash and PowerShell implementations.

.github/workflows/scripts/create-release-packages.ps1

@@ -64,6 +64,7 @@ function Rewrite-Paths {
     $Content = $Content -replace '(/?)\bmemory/', '.specify/memory/'
     $Content = $Content -replace '(/?)\bscripts/', '.specify/scripts/'
     $Content = $Content -replace '(/?)\btemplates/', '.specify/templates/'
+    $Content = $Content -replace '(?:\.specify/){2,}', '.specify/'
     return $Content
 }