docs: align actor terminology with CAMARA (#87)

[caubut-charter]

What type of PR is this?

• documentation

What this PR does / why we need it:

Aligns actor terminology in both specs with CAMARA, per #87. The repository used several competing
labels for the two CAMARA roles — "Network Operator", "API client", and bare "provider" / "client"
— and the casing of "API Consumer" / "API Provider" varied between Title Case and lowercase.

The Commonalities glossary defines API Producer (alternative term API Provider) and
API Consumer, and has no entry for "Network Operator", so the role senses are normalised onto
the CAMARA terms:

• "Network Operator" → "API Provider" wherever it denoted the entity implementing or operating the
  API, including both # Comments for Network Operators headings and the in-text cross-reference
  to one of them.
• "API client" / "API Clients" → "API Consumer" wherever it denoted the role, including both
  # Comments for API Clients headings.
• Bare "provider" / "providers" / "clients" qualified to the full role names.
• Casing normalised to Title Case across specs, modules, user stories and test definitions.

Deliberately not renamed:

• "network-operator-supplied" equipment and the commercial "relationship between a network operator
  and a subscriber". These describe hardware provenance and account relationships, not the API
  role — upstream CAMARA_common.yaml uses "network operator" the same way, in the same sentence
  as "API Consumer" and "API Provider".
• "API client" in the OAuth client_id / resource-ownership sense ("created by the calling API
  client"), which is how the CAMARA API Design Guide uses that phrase. 32 such occurrences are
  preserved.

Glossary repairs made along the way:

• Subscriber was used 40+ times across both specs and defined in neither. Added, noting that
  the specification uses it interchangeably with Service Owner.
• Service was referenced by the Service Owner and Service Site entries in the devices spec
  without being defined there. Added.
• Network Operator is retained but reworded to state the equipment and account relationship
  explicitly instead of duplicating API Provider. It is still referenced by four other glossary
  entries, so deleting it would have left an undefined term.
• "API client operator", a garbled compound occurring exactly once, corrected to API Consumer.
• "Network Client Devices", a dangling resource name used once and defined nowhere, corrected to
  Trust Domain Devices.
• Two list operations named their scoping subject differently ("service owner" vs "subscriber");
  unified on subscriber.

Which issue(s) this PR fixes:

Fixes #87

Does this PR introduce a breaking change?

• Yes
• No

Special notes for reviewers:

• Scoped to the issue title (full audit) rather than the narrowed comment, per maintainer direction.
• Text inside the CAMARA:MANDATORY markers is generated from info-description-templates.yaml
  and is left byte-identical — verified block-by-block against code/common/. The four remaining
  lowercase occurrences all live there and are intentional.
• CPE: already absent repo-wide, so the "make sure to remove CPE" part of [Trust Domains] Align documentation with CAMARA actors and terms #87 needs no change
  and Remove CPE to remove network specific terms #14 can stay closed.
• redocly lint: 0 errors, 9 warnings — unchanged from main.
• One judgement call worth a second opinion: the new Subscriber entry states that this
  specification uses Subscriber and Service Owner interchangeably. That is deliberately
  descriptive rather than normative — if the two are meant to be distinct roles, this entry is the
  place to say so.
• Conflicts with docs: document empty-list, 400/422, and GENERATE credential conventions (#129) #174 (code/API_definitions/*.yaml, TrustDomainDevices.yaml, TrustDomains.yaml)
  and with the Remove incomplete thread specification #65 branch (network-access-domains.yaml, TrustDomains.yaml). All are
  prose-adjacent and mechanical to resolve.

Deferred, not done here: Service Owner casing in the user stories, scope-table wording
("other clients" vs "other API clients"), and an ambiguous "created by" attachment in the
reboot-request list description.

Changelog input

release-note Aligned actor terminology with CAMARA: Network Operator and API client are now API Provider and API Consumer where they denote the CAMARA roles, with added Subscriber and Service glossary entries and two dangling terms corrected.

Additional documentation

This section can be blank.

docs

[clundie-CL]

Minor change requested. Should land this one last after #185

[clundie-CL]

API client -> API Consumer