chore: add Claude Code marketplace manifest for 0.5.4

[StefanoGuerrini]

Summary

Adds .claude-plugin/marketplace.json so the repo is installable as a Claude Code plugin marketplace. Without this file, the existing .claude-plugin/plugin.json is invisible to /plugin install flows; users get "Marketplace not found" errors. Discovered while migrating a developer's Claude Code setup to the merged 0.4.0 plugin after PR #5.

Also aligns .claude-plugin/plugin.json version field with the rest of the repo. The plugin manifest had been stuck at 0.4.0 since the 0.4.0 release even though package.json and memory/pam.version.json bumped through 0.5.0, 0.5.1, 0.5.2, and 0.5.3.

Rebased twice as main absorbed the LLM-retrieval-benchmark (0.5.1), benchmark-threshold-gate (0.5.2), and tight-benchmark-regression-gate (0.5.3) patch slots in succession.

What lands

• .claude-plugin/marketplace.json listing the single pam plugin with "source": "./" so Claude Code discovers the existing root-level plugin manifest.
• .claude-plugin/plugin.json version 0.4.0 -> 0.5.4 (drift fix).
• Version bump 0.5.3 -> 0.5.4 in package.json and memory/pam.version.json; claudeMarketplaceManifest feature flag.
• migrations/0.5.3-to-0.5.4-marketplace-manifest.md to satisfy the migrations:check contiguous chain enforcement.
• CHANGELOG 0.5.4 entry.

Install (after merge)

/plugin marketplace add github:NestDevLab/portable-agent-memory
/plugin install pam@portable-agent-memory

Test plan

• npm test (75/75 pass)
• npm run migrations:check (OK for PAM 0.5.4)
• All three version surfaces aligned at 0.5.4 (package.json, memory/pam.version.json, .claude-plugin/plugin.json)
• pr-reviewer self-review: APPROVE
• Reviewer: confirm marketplace.json schema matches what current Claude Code versions expect
• Reviewer: verify /plugin install pam@portable-agent-memory works against this branch locally

[Copilot]

Pull request overview

This PR updates PAM’s release metadata to 0.5.4 and adds the missing Claude Code marketplace manifest so the repository can be added as a plugin marketplace and the existing pam plugin becomes discoverable/installable via /plugin install.

Changes:

• Adds .claude-plugin/marketplace.json defining a marketplace that exposes the pam plugin with source: "./".
• Aligns version surfaces to 0.5.4 across package.json, memory/pam.version.json, and .claude-plugin/plugin.json, and records the new claudeMarketplaceManifest feature flag.
• Adds a contiguous migration doc (0.5.3 -> 0.5.4) and a CHANGELOG.md entry for 0.5.4.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
package.json	Bumps npm package version to 0.5.4 (used by tooling/server version reporting).
memory/pam.version.json	Bumps PAM version to 0.5.4 and adds features.claudeMarketplaceManifest.
.claude-plugin/plugin.json	Updates Claude Code plugin manifest version to 0.5.4 to match repo versioning.
.claude-plugin/marketplace.json	Adds Claude Code marketplace manifest so /plugin marketplace add can discover/install pam.
migrations/0.5.3-to-0.5.4-marketplace-manifest.md	Documents the 0.5.3→0.5.4 migration to satisfy contiguous migration enforcement.
CHANGELOG.md	Adds 0.5.4 release notes describing the marketplace manifest + version alignment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.