feat(task): add CONFIGURING status for environment setup before execution

[chdominguez]

Summary

• Adds TaskStatus.CONFIGURING, between PENDING and RUNNING.
• BaseTask.run() now sets CONFIGURING on entry instead of jumping straight to RUNNING — previously RUNNING was set the instant the task's coroutine started, before the working directory existed or any environment prep ran.
• BaseExecutor.execute() (the one @final hook every executor funnels through) flips the status to RUNNING once its generic directory setup is done, right before the executor-specific _execute() begins.
• Plugin executors (horus-docker, horus-slurm, horus-terraform, etc., not in this repo) can reuse the same status field to report their own slower setup (image build/pull, VM provisioning, queueing) around their own _execute() — no new API needed, status is already a plain mutable field.
• TUI's exhaustive per-status style/glyph maps updated (the module asserts full coverage, so this was required, not optional).

Ref: temple-compute/tc-os#237

Test plan

• uv run pytest -q — 734 passed
• New test: task status is CONFIGURING during _run, before the executor's _execute runs, then COMPLETED on clean exit
• New test: BaseExecutor.execute sets RUNNING before invoking _execute
• ruff check clean on all touched files

Docs

• No documentation update required