Beach walk tide planner web page

Build a self-contained static web page, with no backend and no external packages, that helps plan beach walks around a bundled tide table. Bundle a hardcoded table of high and low tides for seven consecutive days (at least four tide events per day with times and heights in metres). The page shows a day selector, a simple chart of the tide height over the selected day drawn with inline SVG, and a "safe walking windows" list computing the periods when the tide is below a threshold the person sets with a numeric input (default 1.2 m), each window with its start and end times. Changing the day or the threshold updates the chart and the list without a reload. All controls are usable with the keyboard only, and the layout works at 375 pixels wide with no horizontal scrolling and at 1280 pixels wide. Include a short README explaining the data format and how to open the page. Completion is observable in a real browser: selecting a day redraws the chart, changing the threshold changes the listed windows, and the page lays out at both widths.