relix init: create a project's .relix directory #55

Today everything in docs/design.md §5 assumes a .relix/ directory already exists and was written by hand: the catalog files, profiles.json at the right permissions, the trust record. relix init creates it, so a new project's first query needs no hand-editing.

relix init                                   # .relix/ in the working directory
relix init ~/work/acme --root --profile=staging --output=csv

• Refuses when .relix/ exists (exit 2). Re-running it is never how a project is repaired.
• Trusts what it wrote: records the trust hash (§5.4) after writing, exactly as relix catalog trust would, so the first run shows no "not trusted" warning.
• profiles.json is git-ignored from the start. The .gitignore sits inside .relix/, so init never edits a file of the user's and behaves the same in or out of a repository.
• Outside $HOME it warns that only the working directory's .relix/ is read from there (§5.2).
• Messages go to stderr; init writes nothing to stdout.

Done when

relix init (with and without each flag) produces the tree above at the right permissions, a following relix run in that directory shows no trust warning, and a second init exits 2 without touching anything.