v0.10.1 - Documentation consistency and the Spanish-leak guard

Four documentation/consistency fixes, all found and fixed the same day,
squashed into one release since none had been published individually
(same reasoning as v0.7.0's own three-pieces-in-one-release precedent).

📝 Fixed

• docs/security_model.md claimed PrivateMemory "intentionally retains
  normal Python object identity" - true before v0.9.0, false since: that
  release changed read()/get_all() to return deepcopy()s (same
  hardening already applied to UniversalMemory in v0.8.0), but this
  paragraph was never updated to match. Found by an independent
  installation/upgrade validation exercise, cross-checking docs against
  actual behavior rather than symbol inventory. Corrected, with the "why"
  spelled out instead of just flipping the claim. docs/api_reference.md's
  PrivateMemory method table now explicitly says "deep copy (since
  v0.9.0)" for both read() and get_all().
• sett/services_tts_stt/base.py's module docstring had a Spanish
  paragraph that does not exist in the actual published v0.7.0 source - a
  local-only artifact, never part of any released version. Removed, along
  with five Spanish example strings elsewhere translated to English for
  consistency (SETT is a general-purpose framework; its source should read
  in English throughout).

✨ Added

• docs/SETT_Conventions_v2.md: the framework's own conventions and
  invariants document, published for the first time. Cited from source
  since v0.7.0 ("Convención #N" / SETT_Convenciones_v2.md), but never
  actually shipped - it only existed as a private working note used to
  draft the project's arXiv paper. Translated in full; every citing site
  across CHANGELOG.md and three source files updated to the new name
  and to English ("Convention #N").
• tests/test_no_spanish_in_public_tree.py: a new guard test, same spirit
  and structure as test_no_internal_project_names.py. Scans the public
  tree for text that looks like Spanish (accented vowels, n-with-tilde,
  inverted question/exclamation marks) and fails if it finds any that
  isn't on an explicit, documented allowlist (the framework author's real
  name, the project's own "English, Español, 日本語" paper-language list,
  a couple of necessary illustrative example words/names, and a couple of
  historical CHANGELOG/README entries quoting already-fixed past mistakes
  for the record). Deliberately not a grammar-aware classifier - manual
  review before a release remains the backstop for the rare case of
  Spanish written with zero accented characters - but this catches the
  common case automatically going forward.

✅ Compatibility

Documentation and test-suite only. No code logic changed, no public API changed. 290 tests (up from 280 - 10 new, all in test_no_spanish_in_public_tree.py).