build every agent from the agent-base template

Delete nix/templates/ruth.nix, the ruth nixosConfiguration, module and
toplevel, the hive-c0re managerToplevel option, and the meta flake's
isManager switch with lifecycle::MANAGER_NAME. Every agent, ruth
included, now builds from nix/templates/agent.nix. The template's only
content beyond agent.nix was docs.enable = mkDefault true; docs.enable
is off by default for every agent and ruth's own agent.nix turns it on.

Refs #5377

docs/agent-lifecycle/config-changes.md

@@ -330,8 +330,10 @@ same as any other agent.
 
 Differences from sub-agents:
 
-- `flake.nix` extends `hyperhive.nixosConfigurations.ruth`
-  (vs `agent-base`).
+- Reference docs: her `agent.nix` turns on `services.hyperhive.agent.docs.enable`.
+  Her container builds from `agent-base` like every agent, and the seeded
+  `agent.nix` is the same for every name, so a newly created ruth has no docs
+  until a config PR adds that line.
 - Web UI port via `lifecycle::agent_web_port("ruth")` — same
   FNV-1a hash as every other agent (8100..8999 range).
 - The root agent holds `manage_root_agent` (the swarm UI's setup

docs/turn-loop/README.md

@@ -183,11 +183,10 @@ sibling), one shared `nix/agent-modules/` tree, one service unit
 differences live in the agent's swarm permissions and the broker socket (which tools
 and manager-surface calls each agent receives).
 
-`agent.nix` and `ruth.nix` both import the shared `nix/agent-modules/`.
-`ruth.nix` additionally defaults
-`services.hyperhive.agent.docs.enable` to `true`, so the root/manager
-gets the hyperhive reference docs readable at `$HIVE_DOCS_DIR` by
-default; other agents opt in per `agent.nix` (see
+`nix/templates/agent.nix` is the one entry point every agent builds from, and
+it imports the shared `nix/agent-modules/`.
+`services.hyperhive.agent.docs.enable` defaults to `false` for every agent,
+ruth included; an agent opts in from its own `agent.nix` (see
 [config.md](config.md), "Reference docs").
 
 ### Environment variables set on the unit

docs/turn-loop/config.md

@@ -8,7 +8,7 @@ Absent means the default. (The claude spawn + compaction themselves live in
 ## Reference docs (`services.hyperhive.agent.docs.enable`)
 
 ```nix
-services.hyperhive.agent.docs.enable = true;  # default: false (true for the manager agent)
+services.hyperhive.agent.docs.enable = true;  # default: false
 ```
 
 Makes the hyperhive `docs/` tree available inside the container at a nix
@@ -17,8 +17,8 @@ sentence into the agent's system prompt so it knows the docs exist and
 where to find them. `claude --add-dir` serves the tree so the full
 markdown is readable during every turn.
 
-Enabled by default only for the root/manager agent (`nix/templates/ruth.nix`). Any
-agent can opt in by adding the line above to its `agent.nix`.
+Off by default for every agent, ruth included. An agent opts in by adding the
+line above to its `agent.nix`.
 
 The `docs/` source is a narrow flake input (`hyperhive-docs`) tracked
 separately from the main `hyperhive` flake so editing docs re-locks only