Fix/stablize Robot test infrastructure with data-testid selectors

[khorovatin]

Problems

1. Fragile DOM selectors — PublicMessagingPage.resource used positional
   selectors (nth=7, nth=8, text=Submit >> nth=0/1) that break on any DOM change.
2. Text-coupled page-ready guard — Wait Until Spaceport Page Ready waited for
   text=Protospace Stats, tying test startup to a string that could change.
3. Page Should Contain Text did a full body dump — the keyword grabbed all body
   text and used Should Contain, which never waits; assertions could pass before
   content finished rendering.
4. Charts link selector ambiguity — text=[charts] passes [charts] as a CSS
   attribute selector to Playwright, not a text match.
5. HEADLESS defaulted to False — CI environments have no display server;
   tests would fail or require an Xvfb wrapper.
6. VALID_PASSWORD committed in source — credentials should come from environment
   variables.
7. Debug screenshots overwrote each other — Test Teardown Capture Debug Artifact smoke fired unconditionally on every test and always wrote the same filename,
   leaving only the last screenshot.
8. No one-step setup script — developers had to remember to run pip install
   and rfbrowser init separately.

Solution

Add data-testid attributes to stable DOM landmarks in the React source, then update
all Robot selectors and infrastructure keywords to use them.

Changes

webclient/src/Sign.js

• SignForm — added data-testid='sign-and-vestaboard-input' / data-testid='sign-and-vestaboard-submit'
• VestaboardForm — added data-testid='vestaboard-only-input' / data-testid='vestaboard-only-submit'

webclient/src/Home.js

• Wrapped the entire stats block in <div data-testid="home-stats-section"> for a
  stable page-ready anchor

tests/robot/pages/PublicMessagingPage.resource

• Replaced all positional nth= and text=Submit >> nth= selectors with
  [data-testid="..."] CSS attribute selectors

tests/robot/pages/LandingPage.resource

• Fixed Charts Link Should Navigate to use a:has-text("[charts]") (Playwright CSS)
  instead of text=[charts] (ambiguous CSS attribute selector)

tests/robot/resources/Common.resource

• Wait Until Spaceport Page Ready — now waits on [data-testid="home-stats-section"]
  instead of a text string
• Page Should Contain Text — replaced body dump + Should Contain with
  Wait For Elements State ... visible so assertions properly wait for the element

tests/robot/resources/Variables.resource

• HEADLESS → ${True} (CI-safe default; developers override with -v HEADLESS:False)
• VALID_PASSWORD → %{TEST_PASSWORD=TestPass123!} (env-var with fallback)

tests/robot/tests/smoke.robot

• Test Teardown → Run Keyword If Test Failed Capture Debug Artifact ${TEST NAME}
  — screenshots now fire only on failure and use the test name for unique filenames

tests/robot/setup.sh (new)

• Single script that chains pip install -r requirements.txt + rfbrowser init