agent permissions: one set, tool groups included, set at agent creation

mara on #5170: "dont split caps and perms. its all perms. / dont include
the now empty tool groups / nothing set -> default / also add perms to
agent creation screen".

- hive-sh4re: one `Permission` enum (messaging, meta, inbox, execution,
  web_tools, manage_root_agent) replaces `ToolGroup` and `Capability`;
  `lifecycle`/`forge` are gone. `Permission::default_for` is the default
  for an agent the swarm sets nothing for.
- The record is `{ "permissions": [...] }`. Missing key, unset field or
  no successful read yet = default; `[]` = none; a failed read after a
  good one keeps the last value.
- hive-agent reads its own key every 10s and builds each turn's --tools,
  --allowedTools and MCP config (rewritten before every turn) from it;
  the subagent daemon reads it on each start/continue. Agents get a
  read-only grant on their own key.
- hive-c0re restarts an agent only when its manage_root_agent changes.
  The import now merges meta/capabilities.json and meta/tool-groups.json
  into one list per agent and deletes both; the "import pending, don't
  read" decision is `ImportOutcome::read_allowed`, table-tested.
- swarm-controller: `GET /api/permissions` (names + default) and an
  optional `permissions` on `POST /api/agents`, stored before the job is
  queued. swarm-ui's create-agent form gets a permissions field.
- Deleted: HIVE_TOOL_GROUPS and its forward to the subagent daemon,
  tool_groups.rs, ruth's tool-group seed, the permissions rebuild job
  (PermPayload/WritePermFile/perm_change), the dashboard permissions tab
  and its stale-entries panel.

Part of #5170.

docs/agent-lifecycle/config-changes.md

@@ -244,7 +244,7 @@ bind-mounted **read-only** (`hive-c0re/src/lifecycle/host_config.rs`
 calls `bind_child_agent_dirs` for each entry in
 `topology::all_agents()`). it's a copy to *read* another agent's
 current config — not an editing surface. An agent without the
-capability sees no other agent's config at all.
+permission sees no other agent's config at all.
 
 An agent submits a change to another agent's config the same way it
 makes any other change: **clone the target agent's config repo from the
@@ -252,29 +252,29 @@ forge into its own state dir, commit on a branch, open a PR**, and let
 the operator review and merge it. By design, no second, mount-shaped
 path reaches the same file without the review.
 
-Agents holding the `manage_root_agent` capability (granted per agent in
+Agents holding the `manage_root_agent` permission (granted per agent in
 the swarm's `agent-permissions` record; see
-`docs/process/conventions.md#capabilities`) get additional host-side bind
+`docs/process/conventions.md#permissions`) get additional host-side bind
 mounts via `set_nspawn_flags`:
 
 - `/var/lib/hyperhive/agents/` → `/agents/` (RW) — **every** agent's
-  proposed repo, not just direct children. The capability means "may
+  proposed repo, not just direct children. The permission means "may
   manage any agent", so the mounted set is every agent.
 - `/var/lib/hyperhive/applied/` → `/applied/` (RO) — every agent's
   authoritative applied repo, including `.git`.
 - `/var/lib/hyperhive/meta/` → `/meta/` (RO) — the swarm-wide
   deploy flake.
 
-An agent without the capability only has its direct children's config
+An agent without the permission only has its direct children's config
 dirs.
 
 ⚠️ nspawn bakes bind flags at container start, so hive-c0re restarts
-an agent, after its current turn, when its capabilities change.
+an agent, after its current turn, when its `manage_root_agent` changes.
 
-The root agent holds the capability by default: an agent whose record
-leaves `capabilities` unset gets the hive's default, which is
-`manage_root_agent` for `ruth` and nothing for every other agent.
-Setting `"capabilities": []` for her revokes it.
+The root agent holds the permission by default: an agent whose record
+leaves `permissions` unset gets the default, which includes
+`manage_root_agent` for `ruth` and for no other agent. Setting her
+permissions without it revokes it.
 
 Each proposed repo (`/agents/<n>/config/`) is pre-configured
 with `applied` as a git remote pointing at
@@ -349,8 +349,8 @@ updates the root agent itself.
 
 The system prompt (`hive-agent/prompts/system.md`, rendered by
 `hive-agent/src/prompt.rs`) is the **same for every agent**; what
-varies is which MCP tools it surfaces (gated by tool groups and
-capabilities in `agent.nix`). No `role:manager` block renders only
+varies is which MCP tools it surfaces (gated by the agent's permissions,
+which the swarm sets). No `role:manager` block renders only
 for the root agent. The root agent's role-specific
 behaviour comes from its CLAUDE.md / agent-specific instructions, not
 the system prompt template.