fix: correlate $search ranking ORDER BY to the outer row - #1717

The inherited `$self` composition (SearchAuthors : Authors) made the backlink
resolve to the base entity, which cds-compiler 7.0.1 (CI) rejects during the
relational SQL transform. Make the model self-contained: SearchAuthors owns its
books composition and Books.author points to SearchAuthors directly, so the
$self backlink is unambiguous. Verified compile+to.sql on 7.0.1 and the e2e
ranking still passes on a real HANA.

Relevance ranking is a HANA fuzzy-search feature: with cds.env.hana.fuzzy=false
(and on other DBs) search() yields no score, so the injected ORDER BY sorted by
a constant boolean — useless and a wasted duplicate of the search expression.
Skip the ranking injection unless fuzzy scoring is active. Reverts the fuzzy
fallback like-count assertions accordingly (no ranking ORDER BY, so no doubling).

cds.env.hana.fuzzy is undefined (not false) on every dialect and cds.env.hana
is an always-present config block, so the previous guard injected the ranking
ORDER BY on sqlite/postgres too — where search() is a boolean and the sort is
meaningless. Gate on the active db instead: cds.db?.kind === 'hana' && fuzzy
!== false. Reference tests stub cds.db = { kind: 'hana' } and add negative
tests asserting no ranking on non-HANA and on HANA with fuzzy=false.

- opt out of $search relevance ranking via cds.env.hana.fuzzy.ranked_search = false
- order-by precedence: user-provided ordering first, then the search rank, then
  the runtime's implicit key ordering (entries flagged `implicit: true`, added
  for stable pagination). The rank is inserted before the first implicit entry
  instead of always prepended; the deep-case correlation locates the rank entry
  by its sub-select rather than assuming position 0.

Tests: cqn4sql precedence (rank first / after user / before implicit / mixed)
and opt-out; e2e on HANA that a user `order by` wins over the rank.

With the opt-out cds.env.hana.fuzzy = { ranked_search: false }, `fuzzy` is an
object; the renderer's `fuzzy || 0.7` then rendered `MINIMAL SCORE [object
Object]`. Take the value as the minimal score only when it is a number. Adds an
e2e test that opting out skips the ranking while search still works.

Allow the minimal score to be configured alongside ranked_search via an object
`cds.env.hana.fuzzy = { score, ranked_search }`, in addition to the plain
`fuzzy: <score>`. The search renderer reads the score from `.score` when fuzzy
is an object.

Adds an OData e2e (bookshop admin service) proving the ranked search takes
precedence over the runtime's implicit key ordering: for the same
`$search=Jane&$top=5` request the two matching books flip order when ranking is
turned off via ranked_search: false.