Resolves #58: Adds inline text highlighting support for .stpa file

[Tokessa]

Resolves #58:

Adds four new kinds of inline text highlighting for an .stpa file.

• italic with *
• bold with **
• underline with _
• strikethrough with ~

Markers (*, ~, etc.) are normaly hidden and only appear when the cursor is placed within the highlighted section.
Added a toggle button (top-right corner) to switch between:

• Hidden marker mode (default)
• Visible marker mode

Implemented escaping for marker characters using a backslash, allowing them to be displayed as plain text.

[Copilot]

Pull request overview

This PR adds markdown-like inline highlighting for quoted strings in .stpa files (italic/bold/underline/strikethrough), including cursor-sensitive marker hiding/visibility and escape handling, and ensures diagram labels strip these inline markers when rendered.

Changes:

• Introduces InlineMarkdownDecorator to decorate inline markers in .stpa string literals and adds a UI toggle to show/hide markers.
• Adds shared marker definitions/types and updates markdown export + language server to use/strip marker-aware text.
• Hardens webview icon rendering and makes diagram expansion state immutable.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
extension/tsconfig.json	Adds TS types + paths configuration intended to support Langium typings.
extension/src/utils.ts	Removes UCA_TYPE from utils (moved to utils-classes).
extension/src/utils-classes.ts	Adds UCA_TYPE, marker config types, and shared inline marker definitions.
extension/src/report/md-export.ts	Updates import to new UCA_TYPE location.
extension/src/extension.ts	Wires up inline decorator + editor/title toggle commands and context keys.
extension/src/decorations.ts	New decorator implementing inline marker parsing, hiding, and styling.
extension/src-webview/feather-icons-snabbdom/feather-icons-snabbdom.tsx	Avoids runtime error for unknown icon IDs.
extension/src-language-server/utils.ts	Adds marker stripping + CST raw string extraction for diagram labels.
extension/src-language-server/stpa/diagram/diagram-relationshipGraph.ts	Uses CST-raw string and strips inline markers for node descriptions.
extension/src-language-server/stpa/diagram/diagram-controlStructure.ts	Strips inline markers from edge/IO labels.
extension/src-language-server/diagram-server.ts	Makes expansionState a const map.
extension/package.json	Contributes the new toggle commands and editor/title menu items.
extension/README.md	Documents supported inline highlighting syntax and escaping.

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