Console dev fallback

When no DLT daemon socket is configured and no other log::Log has been registered, the facade (taktora-log facade crate (FEAT_0071)) installs a human-readable console formatter so local cargo run and unit tests produce visible output. Silent drops are explicitly rejected.

Feature: Console dev fallback FEAT_0077
status: approved
satisfies: FEAT_0071
is satisfied by: REQ_0816
is refined by: ADR_0091

When no DLT daemon socket is configured and no other log::Log implementation has been registered, taktora-log::init() shall install a human-readable console formatter so unit tests and local cargo run produce visible output. Silent drops are explicitly rejected.
Requirement: Console fallback installed when no daemon and no other logger REQ_0816
status: approved
satisfies: FEAT_0077

taktora-log::init() shall detect the absence of (a) a configured DLT daemon socket and (b) any pre-existing log::Log implementation, and shall install a console-formatted fallback backend in that case. The fallback shall print one line per record to stderr with level, timestamp, target, formatted message, and structured key-value pairs. The fallback shall be replaceable by any of the other init paths — the fallback is the no-config default, not a forced default.