ensures autoconf client uses mainnet fallback config when server is unreachable or cache is empty

replaces dht.GetDefaultBootstrapPeerAddrInfos with autoconf.FallbackBootstrapPeers to align with kubo's approach

changes '--endpoing' to '--endpoint'

- set all three endpoint types (provider, peer, IPNS) to default to 'auto'
- expand and validate endpoint URLs per flag to support custom configurations
- accept both base URLs (https://example.com) and full URLs with routing paths
- strip routing paths after validation to get base URLs for HTTP client
- validate path matches flag type, error on mismatches with helpful messages
- update stdout to show routing paths explicitly (/routing/v1/providers)
- add spec references to Routing V1 and IPFS Mainnet in docs
- simplify documentation following godoc style

This ensures endpoints only receive requests they support (e.g., cid.contact
only gets provider requests, not peers or IPNS).

when the same base URL appears in multiple endpoint configs
(provider/peer/ipns), create only ONE HTTP client instead of
three separate clients with duplicate connection pools

this was not an issue with cid.contact as it only supported /providers,
but is necessary to future-proof if autoconf provides more routing systems
in the future

implementation:
- client_delegated_routing.go: new file for delegated routing client logic
- collectEndpoints: deduplicates URLs and aggregates capabilities
- createDelegatedHTTPRouters: creates one client per unique base URL
  and registers metrics once for all delegated HTTP clients
- combineRouters: simplified to combine routers without client creation
- clientRouter: moved from server_routers.go to co-locate with client creation

same client instance is reused across routing types when base URL matches,
significantly reducing memory and connection overhead

- add file-level godoc to autoconf.go
- fix parameter shadowing in createAutoConfClient
- add validation for empty strings in collectEndpoints
- add tests for collectEndpoints deduplication logic
- add trailing slash normalization tests

- inline autoconfDisabledError (single use function)
- add newDelegatedRoutingClient helper for consistent HTTP client creation
- use helper in both server and CLI code to ensure consistent options
- rename client_delegated_routing.go to server_delegated_routing.go
- add file-level documentation explaining server-side delegated routing