feat(plugins): add curated plugin catalog module and in-tree catalog dir

- hermes_cli/plugin_catalog.py: loader/search/removed-blocklist for the
  new plugin-catalog/ directory (exact 40-hex SHA pins, https-only repos,
  official/community tiers; invalid entries skipped with a warning)
- plugin-catalog/: admission-policy README, example-plugin seed entry,
  and removed.yaml blocklist

plugin-catalog/README.md

@@ -0,0 +1,60 @@
+# Hermes Plugin Catalog
+
+Curated, Nous-approved Hermes plugins. Each YAML file in this directory
+(except `removed.yaml`) is one catalog entry, discoverable via
+`hermes plugins catalog` / `hermes plugins search` and installable with
+`hermes plugins install <name>`.
+
+## Admission policy
+
+Presence in this directory **is** the trust signal. The rules that keep it
+meaningful:
+
+1. **Human-merged gate.** Entries are added *only* via a PR to the
+   `hermes-agent` repository, reviewed and merged by a maintainer. There is
+   no self-serve registry, no automated ingestion.
+2. **Exact SHA pins are mandatory.** Every entry pins a full 40-character
+   commit SHA. Branches, tags, and short SHAs are rejected by the loader.
+   Installs clone the repository and check out exactly that commit.
+3. **Pin maturity.** The pinned release should be **at least 2 weeks old**
+   at pin time, mirroring the supply-chain policy used for `optional-mcps/`
+   and pyproject dependencies. This gives the community time to notice a
+   compromised release before Hermes ships a pointer to it.
+4. **SHA bumps are new PRs.** Updating an entry's pin is a new PR whose diff
+   (old SHA → new SHA) is re-reviewed like any other change — reviewers are
+   expected to look at the upstream commit range being adopted.
+5. **Owner-or-major-contributor submissions only.** An entry may only be
+   submitted by the plugin repository's owner or a major contributor to it.
+   Drive-by submissions of third-party repos are declined.
+6. **Declared capabilities must match reality.** The `capabilities:` block
+   (tools, hooks, middleware, env vars) must match what the plugin actually
+   registers at the pinned commit. Validation fails the entry otherwise —
+   undeclared capability creep is treated as a security issue.
+
+## Entry schema
+
+```yaml
+name: example-plugin        # [a-z0-9_-]{1,64}, the catalog key
+repo: https://github.com/owner/repo   # https:// only
+sha: <40-hex commit sha>    # mandatory exact pin
+subdir: ""                  # optional path within the repo
+description: One-line description.
+maintainer: OwnerName
+tier: official              # official | community (default community)
+requires_hermes: ">=0.19"   # optional
+docs_url: ""                # optional
+platforms: []               # optional, e.g. [linux, macos]; empty = all
+capabilities:
+  provides_tools: []
+  provides_hooks: []
+  provides_middleware: []
+  requires_env: []
+```
+
+## removed.yaml — the blocklist
+
+When an entry is pulled from the catalog for security or policy reasons, it
+is recorded in `removed.yaml` with a reason and date. The installer refuses
+to install anything matching a removed entry's name or repo URL, so a
+malicious plugin cannot be re-installed from a stale identifier after
+removal. Removals, like additions, land via reviewed PRs.

plugin-catalog/example-plugin.yaml

@@ -0,0 +1,14 @@
+name: example-plugin
+repo: https://github.com/NousResearch/hermes-example-plugins
+sha: 38fe0fb53eff98d477f807432e965429e665ca33
+subdir: ""
+description: Reference example plugins for the Hermes plugin system.
+maintainer: NousResearch
+tier: official
+docs_url: ""
+platforms: []
+capabilities:
+  provides_tools: []
+  provides_hooks: []
+  provides_middleware: []
+  requires_env: []

plugin-catalog/removed.yaml

@@ -0,0 +1,6 @@
+# Blocklist for plugins pulled from the catalog for security or policy
+# reasons. The installer refuses to install anything whose name or repo URL
+# matches an entry here (unless the caller explicitly bypasses the check).
+# Each entry: {name, repo, reason, date}. Removals land via reviewed PRs,
+# same as additions.
+removed: []