refactor: rename authproxy-routes ConfigMap to authbridge-routes for consistency

Problem

The namespace-level default routes ConfigMap is named authproxy-routes, while per-agent routes ConfigMaps use the pattern authbridge-routes-<crName>. This naming inconsistency is confusing:

// Current naming:
AuthproxyRoutesConfigMapName = "authproxy-routes"        // namespace default
"authbridge-routes-" + crName                             // per-agent

The name authproxy is legacy terminology from before the component was renamed to AuthBridge.

Proposed Solution

Rename to use consistent authbridge- prefix:

AuthBridgeRoutesConfigMapName = "authbridge-routes"      // namespace default
"authbridge-routes-" + crName                             // per-agent (unchanged)

Breaking Change Considerations

This is a breaking change for any namespace that has a pre-existing authproxy-routes ConfigMap. Migration options:

Option A: Hard break (v1.0 boundary)

• Rename in one PR
• Document in release notes
• Users must manually rename their ConfigMap

Option B: Deprecation period

1. Support both names (check both ConfigMaps, prefer new name)
2. Log deprecation warning when old name is found
3. Remove support after 2-3 releases

Option C: Automatic migration

• Webhook checks for authproxy-routes, copies to authbridge-routes
• Annotates old ConfigMap with deprecation notice
• More complex, but smoothest UX

Scope

Files to update:

• internal/webhook/injector/namespace_config.go - constant definition
• internal/webhook/injector/volume_builder.go - volume name references
• internal/webhook/injector/container_builder.go - volume mount name
• Documentation: docs/authbridge/demos.md, docs/authbridge-webhook.md
• Test files

Related

• PR #517 added per-agent authbridge-routes-<crName> ConfigMaps
• The inconsistency was noticed during #517 review

Recommendation

Wait until v1.0 release boundary to make this breaking change. Use Option A (hard break) since the namespace-level authproxy-routes ConfigMap is rarely used in practice (most users rely on per-agent routes from AgentRuntime CRDs).

/cc @alantech

Read internal/webhook/injector/namespace_config.go, volume_builder.go, and container_builder.go, then inspect the related tests and the documentation files listed in the issue. First confirm whether the v1.0 boundary should use the hard break or another migration option; done means the selected naming and migration behavior are reflected consistently in code, tests, and docs.