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/api/v0/types.go

@@ -39,7 +39,7 @@ type ServerJSON struct {
 	Description string            `json:"description" minLength:"1" maxLength:"100" doc:"Clear human-readable explanation of server functionality." example:"MCP server providing weather data and forecasts via OpenWeatherMap API"`
 	Title       string            `json:"title,omitempty" minLength:"1" maxLength:"100" doc:"Optional human-readable title or display name for the MCP server." example:"Weather API"`
 	Repository  *model.Repository `json:"repository,omitempty" doc:"Optional repository metadata for the MCP server source code."`
-	Version     string            `json:"version" doc:"Version string for this server. SHOULD follow semantic versioning." example:"1.0.2"`
+	Version     string            `json:"version" minLength:"1" maxLength:"255" doc:"Version string for this server. SHOULD follow semantic versioning." example:"1.0.2"`
 	WebsiteURL  string            `json:"websiteUrl,omitempty" format:"uri" doc:"Optional URL to the server's homepage, documentation, or project website." example:"https://modelcontextprotocol.io/examples"`
 	Icons       []model.Icon      `json:"icons,omitempty" doc:"Optional set of sized icons that the client can display in a user interface."`
 	Packages    []model.Package   `json:"packages,omitempty" doc:"Array of package configurations"`