hive-c0re: render the new agent option paths into generated agent flakes

meta.rs writes each agent's flake, and it still named the pre-move
`hyperhive.*` paths — so every agent rebuild would print a rename
deprecation warning about a line no human wrote and no operator could fix.
A warning nobody can act on trains everyone to ignore the ones that matter,
which is the whole value of the alias shims.

Repoints the FORWARDED_VAR_OPTIONS table and every other emitted option
assignment (otel.*, docs.source, claudeCodePath, github.enable, user.name,
claudeMemoryMaxBytes) to `services.hyperhive.agent.*`, with the test
expectations that pin the rendered text. The flake input named `hyperhive`
(`hyperhive.url`, `hyperhive.inputs.nixpkgs.follows`,
`hyperhive.nixosConfigurations.*`), hive-tier `services.hyperhive.*` paths,
and the `@hyperhive.local` git identity share the word and are untouched.

Also repoints the same option paths where they appear in comments, rustdoc
and runtime message strings across the other crates — a refusal message
naming `hyperhive.allowedRecipients` sends an operator to a path that will
stop existing. Prose under docs/ is deliberately not in this commit.

Refs #4473

hive-agent-sock/src/lib.rs

@@ -16,7 +16,7 @@
 //! signals its own turn loop directly, so hive-c0re is not in either path —
 //! no broker round-trip, no long-poll, no marker files.
 //!
-//! **`extra_mcp`**: the `hyperhive.extraMcpServers` spec + parsing, shared by
+//! **`extra_mcp`**: the `services.hyperhive.agent.extraMcpServers` spec + parsing, shared by
 //! `hive-agent` (the main session's `--mcp-config`) and `hive-subagent-mcp`
 //! (the subagent-eligible subset) — not a socket protocol at all, but this
 //! crate is the natural home since both consumers already depend on it.