feat: track estimated outbound prompt tokens

Record prompt-text estimates for terminal sends and explicit startup
prompts, then expose the totals as a sortable session dashboard column.

test: remove obsolete Eat integration test

fix: handle split output control sequences

Suppress EAT's specific end-of-chunk range error while preserving unrelated
failures.

refactor: simplify session and backend helpers

Remove the redundant backend name wrapper and availability branch. Always
require live sessions when resolving session actions.

docs: bump package version to 0.100.1

fix: allow plan implementation without a region

Let the document implementation command fall back to the whole subject
buffer, matching other document commands. Keep it available in the transient
and cover the no-region path with targeted tests.

fix: hide code-only commands in document mode

Limit the prompt preset and explain-error menu entries to contexts where
their default prompts apply, and cover the catalogue metadata with
regression tests.

fix: use lowercase key for coverage analysis

Update the documented binding and bump the package version to 0.98.4.

test: add dedicated layout coverage

Cover window association, focus switching, selection handling and insertion.

fix: remove duplicate session resume command

Correct the workspace-write key in the customisation example and bump the
package version.