dashboard: render META INPUTS as a full tree with bulk select

Remove the depth-2 cap in walk_meta_inputs so every fetched input
at every depth is surfaced, not just two levels (issue #275). The
uncapped walk needs a guard: a visited-node set makes it a spanning
tree — each fetched node walked once, at its shallowest path — so
shared subtrees don't re-walk and a cycle can't recurse forever.
A two-pass walk (claim a node's direct inputs before descending)
keeps shallow inputs at a shallow path.

Frontend: renderMetaInputs indents each row by its slash-path depth
and shows the leaf segment (full path on hover), plus a select-all /
select-none control so a long input list isn't ticked box by box.

docs/web-ui.md

@@ -107,10 +107,16 @@ the previous process's socket release resolves itself.
    Spawn approval; existing state is reused), `PURG3` (wipes
    state + applied dirs; `POST /purge-tombstone/{name}`).
 4. **M3T4 1NPUTS** — inputs in `meta/flake.lock` the operator can
-   selectively `nix flake update` (hyperhive first, then
-   `agent-<n>` rows). Checking inputs + submitting bumps the lock
-   in `/meta/` and rebuilds the selected agents in sequence; each
-   outcome reaches the manager as a `rebuilt` system event.
+   selectively `nix flake update`, rendered as an indented tree:
+   every fetched input at every depth (`hyperhive`,
+   `hyperhive/nixpkgs`, `agent-<n>`, `agent-<n>/mcp-<x>`, …), each
+   shown once at its shallowest path. `read_meta_inputs` walks the
+   lock graph with a `visited` set — `follows` aliases and rev-less
+   nodes are skipped (issue #275). A `select all / select none`
+   control sits above the tree. Checking inputs + submitting bumps
+   the lock in `/meta/` and rebuilds the selected agents in
+   sequence; each outcome reaches the manager as a `rebuilt`
+   system event.
    `POST /meta-update`. The lock bump + rebuild ripple runs in the
    background; while it does, the panel shows a pulsing "⏳
    meta-update running" banner and the update button is disabled