feat(data): merge several declaration folders into one model

[david-hudec-networg]

Stacked on #190. The first four commits are that PR's defect fixes; review and merge it first. Only the last commit belongs to this one. GitHub cannot express a cross-fork stack, so the base has to be master.

The problem

txc data model convert converts one solution's declarations. A delivery project's data model is never one solution: the product ships several modules that each declare part of a shared table, and the project layers its own on top. In one real project, account draws attributes from five different modules.

Converting each folder separately and concatenating the results does not work — each output declares the same table, so a naive merge keeps one and silently drops the rest. Producing a usable diagram therefore meant 10–25 separate exports and a merge by hand.

The change

--input becomes repeatable:

txc data model convert -i ./src/Modules.Core/Model/Declarations \
                       -i ../TALXIS/src/Areas/Service/Project/Model/Declarations \
                       --target dbml

The seam already existed. ParseModel(List<string>) builds one Module per zip and calls ParseModules once; folders never got the same treatment. This extracts folder→Module and zip→Module and routes both through it, so inputs can be mixed — folders, project files and .zip in one invocation.

Merge policy

Where two inputs declare the same attribute:

• First input wins, so the result is deterministic in the order the caller gave, and the caller controls that order. Documented in the option's own description.
• A divergent type warns rather than aborting. Several modules extending one shared table is the normal case for a layered product, not an error worth failing a conversion over.
• Text lengths widen, never narrow — a downstream consumer breaks on too little room, not too much.

This also fixes a latent bug: Table.ParseMultipleRowsFromXml appended rows with no dedup by name. Harmless with a single input; routine with several.

Two things that fell out

Modules are now named after the folders that own their declarations, so a merged diagram attributes each table to its source instead of rendering an empty // comment.

Module.Colorhex became a computed property. Assigned in the constructor, it was evaluated before an object initializer had set ModuleName — so every module came out the same colour, which is invisible with one input and obvious with ten.

Back-compat

The single --input form, the no-input default to the working directory, and the existing ConvertModel(string, …) / ParseModelFolder(string) signatures all behave as before — the latter two are kept as thin wrappers. Verified across three solutions × five targets (dbml, sql, plainsql, edmx, ribbon): all exit 0 and are idempotent by hash.

Measured

The ten declaration folders behind one real project, in a single invocation:

time	1.7s
tables / refs	211 / 408
columns / enums	5005 / 577
distinct module colours	11
@dbml/core	PARSE_OK
merge warnings	0

Tests

tests/TALXIS.CLI.Tests/Data/DataModelConverter/MultipleInputMergeTests.cs — seven tests over in-memory Modules and temp folders, no new dependencies: two modules merge into one table with both columns; a repeated attribute produces one column; a conflicting type keeps the first; lengths widen regardless of input order; modules colour apart; and one folder through the list entry point matches the single-folder entry point.

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