refactor(core): 034 Phase 1 — mechanical debt cleanup (#129, #132)

[lxsaah]

Summary

Phase 1 of the 034 technical-debt review — the mechanical, zero-behavior-change cleanup. One PR for the whole phase (per the "one PR per phase" plan), structured as one commit per work item so it reviews cleanly. Breaking changes are accepted (decision 2026-06-09).

Closes #129. Closes #132.

Net: +177 / −638 lines across core, adapters, and the MQTT/KNX connectors.

Commits (one per work item)

Commit	Item
delete dead Database wrapper, adapter aliases, .link()	§3.8 — Database<A>, TokioDatabase/EmbassyDatabase, deprecated RecordRegistrar::link() (all zero-user)
unify DbError on alloc::String (#129)	§3.1.1 — one variant shape on every target; thiserror derives Display/Error unconditionally; no_std numeric-code Display table deleted
unify std/alloc imports; merge RuntimeContext impls	§3.1.2 — dual use std::… / use alloc::… pairs → one use alloc::…; duplicated RuntimeContext impl blocks merged
crate-private log_*! macros replace tracing gates	§3.1.3 — 62 per-site #[cfg(feature = "tracing")] gates → log_debug!/log_info!/log_warn!/log_error!
struct-ify OutboundRoute	§3.10 — 5-tuple alias → struct with named fields
flatten subscribe_any; O(1) by_key lookup	§3.8/§3.10 — subscribe_any infallible; O(n) keys().find() → O(1) get_key_value
drop vestigial tokio dependency	§3.1.3 — std no longer pulls tokio into every build (tests cover it via dev-deps)
changelog entries	Keep-a-Changelog entries (root + 5 crates)
import ToString in buffer traits test module	no_std test-build fixup

Breaking changes (accepted)

• no_std DbError: _field: () placeholders become the real String fields; Display now prints full messages instead of Error 0xNNNN codes; DbError now implements core::error::Error. Std variant shapes/messages unchanged.
• Removed: Database<A>, TokioDatabase, EmbassyDatabase, RecordRegistrar::link().
• ConsumerTrait::subscribe_any returns Box<dyn AnyReader> (was DbResult<…>).
• OutboundRoute is a struct, not a 5-tuple.
• aimdb-core's std feature no longer enables a tokio dependency; thiserror is now a mandatory (no_std) dependency; DbError::{runtime_error, permission_denied, record_key_not_found} are now pub (+ new missing_configuration).

Verification

• make check — fmt, clippy (full feature matrix), test, test-embedded (thumbv7em-none-eabihf), test-wasm, deny — all pass
• make examples — all example crates build
• Acceptance greps from both issues: no _field: () placeholders, no use std::{ dual imports, no tracing gates outside src/log.rs, cargo tree shows no tokio in normal deps, no Database/.link() references.

Out of scope (other issues)

#130 (builder de-Any, registrar lifetimes), #131 (R removal), #133 (panic-free validation), #134 (MQTT knobs out of core).

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