tracing-log bridge

Keeps existing tracing::* emitters (notably taktora-executor-tracing) working without rewrite by capturing their events as log::Record through the same active backend (taktora-log facade crate (FEAT_0071)).

Feature: tracing-log bridge for existing tracing emitters FEAT_0078
status: approved
satisfies: FEAT_0071
is satisfied by: REQ_0805
is refined by: ADR_0090

Existing tracing::* emitters (notably taktora-executor-tracing) must keep working without rewrite. The bridge captures tracing events as log::Record so they flow through the same active backend as direct log::* calls. No business-code changes are required when a crate moves between tracing and log.

Requirement: tracing-log bridge installed at init REQ_0805
status: implemented
satisfies: FEAT_0078
is verified by: TEST_0805
links outgoing: BB_0090, TEST_0805

taktora-log::init() shall install the tracing-log bridge (LogTracer::init() or equivalent) so events emitted via tracing::info! / tracing::warn! / tracing::error! appear as log::Record values delivered to the active LogSink. The bridge shall be installed exactly once and shall not double-emit when a tracing-subscriber is also registered.