feat(cobol-to-java): BMS screens -> view models, handlers and web views (#3619)

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Closes #3619. Part of #3625.

What

CICS programs talk to users through 3270 screens defined in BMS maps. The verified skeleton already joins every SEND / RECEIVE MAP to its map's fields (screen_bindings, ledger field BMS screen fields). This PR turns those facts into the application's screen layer.

Always (when a program uses screens):

• dto.screen.<Map>Screen, one view model per map:

  • a property per named field, with a Javadoc citing its BMS line, POS, LENGTH, ATTRB and symbolic-map names;
  • LAYOUT: every field in screen order, labels included;
  • fromValues / screenValues for form binding.

  It follows the config's Lombok or plain style, and stays a class even under dto_style: record, because a form bean must be mutable.

• ScreenField / ScreenCell / ScreenModel: ScreenModel.screenCells() turns any screen into positioned cells (labels, outputs, input boxes, OCCURS expanded). The layout logic is compiled Java, not template code.

• Service handlers:

  • render<Map>(screen) per SEND, and submit<Map>(input, aid) per RECEIVE, where aid is the key pressed (EIBAID). Each cites its COBOL lines, and the business logic is a TODO.
  • A map that no single BMS source defines gets a TODO naming the candidates and, when the mapset is known, the maps it does define.

ui.flavour (new config key, default none):

flavour	adds
none	nothing more
openapi-only	a @RestController per program: GET /api/v1/<program>/screens/<map> renders, POST submits with @Valid (@Size from LENGTH, @Pattern from ATTRB=NUM); springdoc 2.5.0 serves /v3/api-docs and Swagger UI
thymeleaf	a @Controller per program, plus one generic templates/screen.html that draws any screen on its 24×80 grid from its cells, with ENTER / PF3 / CLEAR buttons

The needed starters are added to the Maven and Gradle builds. A flavour requires features.services and features.rest_controllers.

Found along the way: a bug in the CBSA sample

BNK1CCS.cbl:236, on CLEAR, sends MAP('BNK1CCM'), which is the mapset's name; its only map is BNK1CC, used by every other SEND and RECEIVE in the program. The generated service says so: … no single BMS source defines it (candidates: none in the repository); mapset BNK1CCM defines BNK1CC.

Evidence

corpus	view models	fields	SEND / RECEIVE sites	unresolved
CardDemo	21	585	26 / 21	0
CBSA	9	130	27 / 9	1 (the bug above)
GENAPP	5	74	43 / 9	0

• Compiles: 45/45 (CardDemo, CBSA and GENAPP × 15 configs, including the new ui-thymeleaf and ui-openapi-plain). Preflight now also compiles CardDemo ui-thymeleaf.
• Runtime, not just compile. I ran throwaway tests, not committed, in generated CardDemo projects:
  • thymeleaf: the sign-on page renders with its labels and title, USERID is an 8-character input, and a PF3 submit round-trips through the service;
  • openapi-only: JSON render and submit work; an over-long USERID gets 400 from @Valid;
  • the whole generated app boots on H2: /v3/api-docs lists the screen's GET and POST, with maxLength: 8 from the BMS LENGTH.
• Default config: nothing else moves. The only changes are the new dto/screen package and the services of screen programs (21 / 9 / 5). zECS, zopeneditor and DSF are unchanged, and the refraction snapshots are unchanged.
• Tests: full suite 11,785 passed. test_bms_screens.py runs a real scan with a label, IC, NUM, DRK and OCCURS fields, a continued BMS macro, an unresolvable map and a mapset-named map, across all three flavours, plus the config validation, manifest and worklist.

Paper trail

• traceability.json: screen-view-model, screen-field (BMS line and position), screen-send, screen-receive and screen-endpoint entries.
• Migration worklist: the handlers' TODOs are business logic, and unresolved maps are fact-gaps.
• Guardrail: the view models are inventoried like any DTO, so an agent adding a field is flagged layout-changed.

🤖 Generated with Claude Code

https://claude.ai/code/session_017ZsVaAkb86P5r5JXDC2Y9g

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