Resolve the fallback HEAD only for a branch that needs it

[masawada]

Why

• eda remove resolved the HEAD of the invoking worktree and of the primary checkout before any removal, even with --force, which judges nothing against a base.
• When the primary checkout is on an unborn branch (after git switch --orphan), that resolution failed, so a forced removal and a removal judged by a resolvable upstream both failed with "cannot resolve HEAD". The WorktreeRemove hook failed the same way.

What

• --force skips the base resolution entirely.
• Otherwise the HEADs are still resolved once when the command starts, but a failure is kept in the base and reported only for a branch that falls back to that HEAD. The hook does the same for the primary HEAD.
• Tests cover forced and upstream-based removal with an unborn primary HEAD, fallback failures for both the primary and invoking HEADs, multiple branches, forced removal without an invoking worktree, and the hook.