rux get: no route for building components; --help lists collections that don't exist

[pfmephisto]

Found while building the MCP gateway (PR #349, #267).

Two related gaps in the path-based DB access:

1. Building components have no `rux get` route. The real collections are `clouds, frames, labels, log, materials, meshes, panoramas, projects` — components are only reachable via `rux export csv`, which the MCP gateway now uses as a documented stopgap (`tools/rux-mcp/src/rux_mcp/components.py`).
2. `rux get --help` is stale: it advertises `components` and `passports` as collections, but neither resolves (passports actually live under `materials`).

Fix: add a `components` router (`apps/rux/src/database/` — the 8 existing `*_router.cpp` files are the template, and since #249/#345 they are linkable from tests), and regenerate the help text from the actual router table so it cannot drift again.

category=CLI estimate=4h

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