security: fix open redirect and add small hardening (#1227)

## What this does

Fixes an open redirect plus a handful of small, mostly-invisible
hardening changes around it.

## What's in it

- **The fix**: trailing-slash redirects no longer let `//evil.com/`
redirect off-host.
- **SSRF block** on the DNS/HTTP namespace verification — refuses to
dial loopback, RFC1918, link-local, multicast, CGNAT, or
IP-literal/single-label \"domains\".
- **Slow-client guard**: `ReadTimeout` and `IdleTimeout` on the HTTP
server (no `WriteTimeout` — would risk cutting off legitimate
multi-package publishes).
- **Defence-in-depth headers** on the UI (`/`) and 404 responses.
- **5xx responses** stop leaking raw DB error text to clients (logged
server-side instead).
- **Search filter** stops treating `%` and `_` as wildcards.
- **Validators**: PyPI/NuGet identifiers URL-escaped before fetching;
MCPB no longer follows redirects.
- **Misc**: `Version` field bounded to 255 chars; logs quote user input;
`BlockedNamespaces` denylist now catches subdomain claimants.

Each change is its own commit so they can be reviewed (or reverted)
independently.

## Test plan

- [ ] CI green
- [ ] Synthetic publish in staging for each package type (npm, pypi,
nuget, oci, mcpb) — confirms validator changes don't regress
- [ ] Quick browser check of `/` after deploy to confirm UI still loads
with the new CSP
- [ ] `curl https://<host>//evil.com/` — confirm the open redirect is
closed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pkg/model/types.go

@@ -35,7 +35,7 @@ type Package struct {
 	//   - For MCPB: direct download URL
 	Identifier string `json:"identifier" minLength:"1" doc:"Package identifier - either a package name (for registries) or URL (for direct downloads)" example:"@modelcontextprotocol/server-brave-search"`
 	// Version is the package version (required for npm, pypi, nuget; optional for mcpb; not used by oci where version is in the identifier)
-	Version string `json:"version,omitempty" minLength:"1" doc:"Package version. Must be a specific version. Version ranges are rejected (e.g., '^1.2.3', '~1.2.3', '>=1.2.3', '1.x', '1.*')." example:"1.0.2"`
+	Version string `json:"version,omitempty" minLength:"1" maxLength:"255" doc:"Package version. Must be a specific version. Version ranges are rejected (e.g., '^1.2.3', '~1.2.3', '>=1.2.3', '1.x', '1.*')." example:"1.0.2"`
 	// FileSHA256 is the SHA-256 hash for integrity verification (required for mcpb, optional for others)
 	FileSHA256 string `json:"fileSha256,omitempty" pattern:"^[a-f0-9]{64}$" doc:"SHA-256 hash of the package file for integrity verification. Required for MCPB packages and optional for other package types. Authors are responsible for generating correct SHA-256 hashes when creating server.json. If present, MCP clients must validate the downloaded file matches the hash before running packages to ensure file integrity." example:"fe333e598595000ae021bd27117db32ec69af6987f507ba7a63c90638ff633ce"`
 	// RunTimeHint suggests the appropriate runtime for the package