Migrate model layer to b8 models (2.3.5)

[sultann]

Implements #525 — migrate the model layer to b8 models, ahead of the framework swap.

Status: foundation complete & green; the model conversion itself is the next commit and needs a design check (below) before I execute it — hence draft.

Done & verified (commits so far)

1. src/ → includes/ consolidation — 35 files moved as tracked renames, autoload narrowed to includes/, every class verified resolving to the new path.
2. PHPUnit harness + baseline suite (from tests/phpunit-baseline, bytekit-native) — green: 42 tests, 130 assertions on the current framework-model code. This is the behavior oracle the migration must keep green.
3. byteever/models wired (dev-master) with Strauss prefixing → WooCommerceSerialNumbers\B8\Models\Model; baseline still 42 green with it installed.

Remaining: the model conversion (Key, Activation) — plan + landmines

The conversion surface is small (~34 accessors, ~20 static/CRUD calls) but carries real divergences I want your call on before writing it:

• insert() param order — framework-model insert($data, $wp_error); b8 insert($data, $search, $wp_error). functions.php:165 Key::insert($args, $wp_error) must become Key::insert($args, null, $wp_error) or it silently passes $wp_error as $search.
• get() → find() — Key overrides get() to encrypt serial_key before lookup (Key.php:583). b8 has no get(); this override + its call sites (self::get, parent::get, functions.php) convert to find().
• prepare_where_query() — framework-model's custom WHERE hook has no direct b8 equivalent; b8 uses fluent where() + the query_clauses filter. Key's custom query logic (encrypted-key lookup, custom clauses) needs re-implementing against b8's pipeline. This is the main re-write and the highest-risk piece.
• view context — Activation getters default to 'view', which in framework-model applies a per-prop filter; b8 get() doesn't. Need to preserve (filter) or confirm unused.
• save() return — framework-model returns true|WP_Error; b8 returns static|WP_Error. Call sites checking true === save() must move to is_wp_error().
• Accessors — get_prop/set_prop/set_date_prop (34 sites). Decision needed: faithful instance adapters on the SN Model base (preserves contract + view filtering, smaller/safer, but a transitional adapter) vs full native conversion to $this->get()/set() (aligns with the convert-to-native preference, ~34 edits, drops view filtering unless re-added).

Gate before this leaves draft

• Baseline stays 42 green through the conversion; add result-equivalence (old vs new Key) + pagination (paged) tests.
• Build swap (esbuild/sass + autoprefixer, same paths) lands after the model conversion.
• Tag byteever/models 1.0.0 and pin (drop dev-master) before release.