feat(plugins): tabulate plugin list output (#23727)

## Summary
- render `codex plugin list` as one table per marketplace with the
marketplace manifest path shown above each table
- surface the installed plugin version in the CLI output by threading
`installed_version` through marketplace listing state
- narrow the system-root exemption so only known bundled/runtime
marketplaces skip missing-manifest failures, and keep `VERSION` empty
for cached-but-unconfigured plugins

## Rationale
The plugin list UX was hard to scan as a flat list and did not show
which installed version was active. This change makes the CLI output
easier to read in the real multi-marketplace case, keeps the plugin path
visible, fixes the Sapphire regression where bundled/runtime marketplace
roots were blocking `plugin list`, and addresses the two review findings
that came out of the follow-up deep review.

## Key Decisions
- kept the CLI output grouped per marketplace instead of one global
table so the marketplace path can live with the rows it owns
- kept `VERSION` as the installed version, which means it is empty until
a plugin is actually installed
- handled the bundled/runtime regression in the CLI snapshot validation
path rather than widening app-server protocol or changing marketplace
loading behavior
- narrowed the exemption to known system marketplace names plus expected
system paths, so user-configured marketplaces under those directories
still fail loudly
- gated `installed_version` on actual installed state so `VERSION`
cannot show stale cache state for `not installed` rows

## Validation
- `just fmt`
- Sapphire: `cargo test -p codex-cli --test plugin_cli` (`14 passed; 0
failed`)
- Sapphire smoke test: bundled/runtime roots still work
  - `cargo run -q -p codex-cli -- plugin add sample@debug`
  - `cargo run -q -p codex-cli -- plugin list`
- verified the bundled/runtime-root scenario no longer errors and shows
the expected marketplace table output
- Sapphire smoke test: custom marketplace under bundled path still
errors
- verified `failed to load configured marketplace snapshot(s)` for
`custom-marketplace`
- Sapphire smoke test: cached-but-unconfigured plugin hides version
- verified `sample@debug not installed` renders with an empty `VERSION`
column

## Sample Output
```text
/tmp/custom-marketplace/plugin.json
NAME          VERSION  STATUS         DESCRIPTION
sample@debug  1.0.0    enabled        Debug sample plugin
other@local            not installed  Local development plugin
```

codex-rs/core-plugins/src/manager_tests.rs

@@ -1599,6 +1599,7 @@ enabled = false
                     id: "enabled-plugin@debug".to_string(),
                     name: "enabled-plugin".to_string(),
                     local_version: None,
+                    installed_version: Some("local".to_string()),
                     source: MarketplacePluginSource::Local {
                         path: AbsolutePathBuf::try_from(tmp.path().join("repo/enabled-plugin"))
                             .unwrap(),
@@ -1617,6 +1618,7 @@ enabled = false
                     id: "disabled-plugin@debug".to_string(),
                     name: "disabled-plugin".to_string(),
                     local_version: None,
+                    installed_version: Some("local".to_string()),
                     source: MarketplacePluginSource::Local {
                         path: AbsolutePathBuf::try_from(tmp.path().join("repo/disabled-plugin"),)
                             .unwrap(),
@@ -1738,6 +1740,7 @@ plugins = true
             id: "default-plugin@debug".to_string(),
             name: "default-plugin".to_string(),
             local_version: None,
+            installed_version: None,
             source: MarketplacePluginSource::Local {
                 path: AbsolutePathBuf::try_from(tmp.path().join("repo/default-plugin")).unwrap(),
             },
@@ -2170,6 +2173,7 @@ enabled = true
             id: "toolkit@debug".to_string(),
             name: "toolkit".to_string(),
             local_version: None,
+            installed_version: Some("local".to_string()),
             source: MarketplacePluginSource::Git {
                 url: missing_remote_repo_url,
                 path: Some("plugins/toolkit".to_string()),
@@ -2287,6 +2291,7 @@ plugins = true
                 id: "linear@openai-curated".to_string(),
                 name: "linear".to_string(),
                 local_version: None,
+                installed_version: None,
                 source: MarketplacePluginSource::Local {
                     path: AbsolutePathBuf::try_from(curated_root.join("plugins/linear")).unwrap(),
                 },
@@ -2582,6 +2587,7 @@ enabled = false
             id: "dup-plugin@debug".to_string(),
             name: "dup-plugin".to_string(),
             local_version: None,
+            installed_version: None,
             source: MarketplacePluginSource::Local {
                 path: AbsolutePathBuf::try_from(tmp.path().join("repo-a/from-a")).unwrap(),
             },
@@ -2613,6 +2619,7 @@ enabled = false
             id: "b-only-plugin@debug".to_string(),
             name: "b-only-plugin".to_string(),
             local_version: None,
+            installed_version: None,
             source: MarketplacePluginSource::Local {
                 path: AbsolutePathBuf::try_from(tmp.path().join("repo-b/from-b-only")).unwrap(),
             },
@@ -2698,6 +2705,7 @@ enabled = true
                 id: "sample-plugin@debug".to_string(),
                 name: "sample-plugin".to_string(),
                 local_version: None,
+                installed_version: None,
                 source: MarketplacePluginSource::Local {
                     path: AbsolutePathBuf::try_from(tmp.path().join("repo/sample-plugin")).unwrap(),
                 },