feat: read the dispatch table through nova_routing_trie

[Taure]

Companion to novaframework/nova#405, which replaces routing_tree with an in-tree, opaque nova_routing_trie.

rebar3 nova routes, audit, openapi and doctor all -include_lib("routing_tree/include/routing_tree.hrl") and destructure #host_tree{}, #routing_tree{}, #node{} and #node_comp{}. Those records no longer exist, so all four crash against a current Nova.

rebar3_nova_dispatch is now the only module that talks to the routing table. It uses nova_routing_trie:routes/1 — the supported introspection API, since the trie is opaque — and hands the tasks a flat list of {Path, Method, Payload}. That also removes a fair amount of duplication: the three collectors had each grown their own near-identical node recursion and segment formatting.

Behaviour notes:

• Paths arrive already rendered, so :id is rewritten to {id} for the OpenAPI-shaped reports rather than reconstructed from node flags.
• A trailing [...] has no OpenAPI equivalent and is dropped from those paths.
• rebar3 nova routes prints a flat, sorted listing with the handler and any host scoping. The old output was a box-drawing tree over routing_tree's node structure, which the new table does not expose and which said nothing about which handler served a route.
• Status-code routes stay out of audit and openapi, as before, and routes shows them as (status NNN).

rebar3_nova_dispatch_SUITE builds a real dispatch table with nova_router and checks each task can read it, including the websocket, static and status-code shapes the old walkers special-cased. Verified locally with _checkouts pointing at the Nova branch: 37/37 CT, xref clean, erlfmt clean.

This cannot merge until Nova releases with nova_routing_trie — {deps, [nova, fs]} is unpinned, so CI here still resolves the current hex Nova and will fail until then.