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-subagent-mcp/src/mcp_config.rs

@@ -1,5 +1,5 @@
 //! Builds a subagent's own filtered `--mcp-config`: only
-//! `hyperhive.extraMcpServers` entries with `availableToSubagents = true`
+//! `services.hyperhive.agent.extraMcpServers` entries with `availableToSubagents = true`
 //! (see `hive_agent_sock::extra_mcp::ExtraMcpServer::available_to_subagents`) ever reach
 //! a subagent's claude invocation, plus this daemon's own two-tool signal
 //! surface. Everything else — the built-in hyperhive

hive-subagent-mcp/src/session.rs

@@ -814,7 +814,7 @@ fn validate_name(name: &str) -> anyhow::Result<()> {
         .map_err(|e| anyhow::anyhow!("invalid subagent name {name:?}: {e}"))
 }
 
-/// Env var carrying the nix-configured `hyperhive.availableModels` as a
+/// Env var carrying the nix-configured `services.hyperhive.agent.availableModels` as a
 /// comma-separated list, forwarded onto this daemon's unit by
 /// `nix/agent-modules/mcp.nix` the same way `HIVE_TOOL_GROUPS` is.
 const AVAILABLE_MODELS_ENV: &str = "HIVE_AVAILABLE_MODELS";