chore: bump version to 0.6.6

Release v0.6.6 — Stage 11, report() display quality (#260–#275). A batch of
display-layer correctness and consistency fixes across every result type:

- crop-off in non-TTY output so stars/CI columns are never dropped (#260)
- empty-header suppression; legends/notes as plain text (#261)
- `_fmt` fixed-decimal String formatter — no ragged decimals, no `-0.0` (#262)
- dust/reference-row guard + degenerate-fit banner (#263); horizon dedup (#264)
- shared display conventions: `_label`/`_yesno`/`_fmt_pvalue`/`(Intercept)` (#265)
- report() dispatches + bare-return display wrappers (#266); content standard —
  every report ends with an estimates table (#267)
- display-dialect unification + package-wide report(io, x) io-plumbing (#268)
- CI/quantile/SE label fixes (#269); johansen rank off-by-one (#270)
- panel between/overall-R² estimation fix (#271); GLP boundary flag (#272)
- display one-offs batch (#273); compilable LaTeX booktabs backend (#274)
- goldens + invariants regression harness locking the display layer (#275)

(No README version line; display-only — no src/plotting changes, committed plots
unchanged.)

Claude-Session: https://claude.ai/code/session_01QZizX88NDsBZrBgdqPcLQp
