feat(cli+sdk): consolidate default paths under ~/.config/loseit

[phitoduck]

Summary

Move backup root + trash file under ~/.config/loseit/ so they sit next to config.yaml and the auth token. Previously they followed XDG strictly (backup + trash in ~/.local/share/loseit/, config in ~/.config/loseit/), which split ~3 files across two top-level directories for no real benefit on a single-user workstation.

New defaults

~/.config/loseit/
  config.yaml
  token
  backup/                  ← was ~/.local/share/loseit/backup/
  trash.jsonl              ← was ~/.local/share/loseit/trash.jsonl

Override mechanisms (in addition to existing CLI flags)

Surface	Env var	CLI flag
Backup root	LOSEIT_BACKUP_ROOT	--root
Trash file	LOSEIT_TRASH_FILE	--trash-file

Typer's envvar= mechanism makes --help self-documenting:

--trash-file  PATH  Source trash file. Default:
                    ~/.config/loseit/trash.jsonl (override
                    via $LOSEIT_TRASH_FILE).
                    [env var: LOSEIT_TRASH_FILE]

Verification

Smoke-tested all four paths:

$ loseit backup --start 2025-12-01 --end 2025-12-31 --dry-run | grep root
  root:               /Users/ericriddoch/.config/loseit/backup     ← new default

$ LOSEIT_BACKUP_ROOT=/tmp/loseit-envvar-test loseit backup ... --dry-run | grep root
  root:               /tmp/loseit-envvar-test                       ← env var wins

$ loseit backup --root /tmp/explicit-cli ... --dry-run | grep root
  root:               /tmp/explicit-cli                             ← CLI flag wins

Full unit suite: 276/276 green (4 tests had hard-coded ~/.local/share/loseit/ path expectations; updated to match).

What this does NOT do

• No automatic migration. Existing backups under ~/.local/share/loseit/backup/ stay where they are. Users can:
  • re-run loseit backup against the new default (resume-safe, just refetches the missing year-dirs); or
  • mv ~/.local/share/loseit/backup ~/.config/loseit/backup to keep the existing archive.
• Existing ~/.local/share/loseit/trash.jsonl is also left in place. Users who want to keep the old trash history: mv ~/.local/share/loseit/trash.jsonl ~/.config/loseit/trash.jsonl.

Test plan

• Reviewer reads the diff (mostly path string swaps).
• Reviewer confirms --help text mentions the new env vars.
• Reviewer runs loseit backup --dry-run and confirms the printed root: is under ~/.config/loseit/backup.