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-matrix-mcp/src/accounts.rs

@@ -8,7 +8,7 @@
 //! `<state>/matrix-sdk-state`) and the daemon-wide `HIVE_MATRIX_URL`.
 //! Any **extra** accounts come from the `HIVE_MATRIX_ACCOUNTS` env var
 //! (JSON, written by the nix harness module from
-//! `hyperhive.matrixAccounts`) and are appended after `main`.
+//! `services.hyperhive.agent.matrixAccounts`) and are appended after `main`.
 //!
 //! So a single-account agent (no `HIVE_MATRIX_ACCOUNTS`) gets exactly
 //! `main` — zero config, same behaviour as before: omitting `account` on